I'm currently trying to work with vectors / deques of structures. Simple example of the structure...
struct job {
int id;
int time;
}
I want to be able to search through the structure to find the job that matches the time, remove it from the structure and continue to check for other ids in that structure. Sample code...
<vector> jobs;
<deque> started;
for (unsigned int i = 0; i < jobs.size(); i++)
{
if (jobs.at(i).time == time)
{
started.push_back(jobs.at(i));
jobs.erase(jobs.begin() + i);
i--;
}
}
time++;
This works how I want it to but it also seems very hacky since I'm adjusting the index whenever I delete and I think it's simply because I'm not as knowledgeable as should be with data structures. Anyone able to give me some advice?
NOTE - I don't think this is a duplicate to what this post has been tagged to as I'm not looking to do something efficiently with what I already have. To me, it seems efficient enough considering I'm reducing the size of the deque each time I get what I need from it. What I was hoping for, is some advice on figuring out what is the best data structure for what I'm attempting to do with deques, which are likely not meant to be handled as I'm handling them.
I could also be wrong and my usage is fine but just seems off to me to.
Well, I always knew that this talk would come in handy! The message here is "know your STL algorithms". With that, let me introduce you to std::stable_partition.
One thing you can do is use just one single vector, as follows:
using namespace std;
vector<job> jobs;
// fill the vector with jobs
auto startedJobsIter = stable_partition(begin(jobs), end(jobs),
[=time](job const &_job) { return _job.time == time; });
Now, everything between begin(jobs) and startedJobsIter satisfy the condition, while everything from startedJobsIter and end(jobs) does not.
Edit
If you don't care about the relative ordering of the items, then you could just use std::partition, which could be even more performant, because it would not preserve the relative ordering of the elements in the original vector, but will still divide it into the two parts.
Edit 2
Here's an adaptation for older C++ standards:
struct job_time_predicate {
public:
job_time_predicate(int time) : time_(time) { }
bool operator()(job const &the_job) { return the_job.time == time_; }
private:
int time_;
};
int main()
{
using namespace std;
int time = 10;
vector<job> jobs;
// fill that vector
vector<job>::iterator startedJobsIter =
stable_partition(jobs.begin(), jobs.end(), job_time_predicate(time));
}
Related
I have developed a program in C++11 and I want to speed up the performance.
I will use a simple example to show the structure of the program (not complete).
//main.cpp
#include "a.h"
int main()
{
std::vector<a> a_container;
for (auto i=0; i< 10K; i++)
{
a a_obj;
a_container.push_back(a_obj);
}
for(time = 1; time< long_time; time++)
{
//i used openmp here already
for (auto i=0; i< 10K; i++)
{
a_container[i].dosomething();
}
for (auto i=0; i< 10K; i++)
{
a_container[i].update();
}
}
return 1;
}
//a.cpp
//a.h
#include "b.h"
class a
{
int d;
b b_obj;
int dosomething();
}
//b.cpp
//b.h
class b
{
int c;
double d;
int dosomething();
}
So in order to speed up the program, I want to use both MPI and OpenMP, mainly for the loop (could be up to 1 million~1 billion instances).
The class object a and b both contain complex member variables (standard and other containers, etc.) and functions.
By using OpenMP, I can take advantage of one HPC node with all cores/threads. But if I want to use MPI, I need to distribute all the instances to many nodes.
I haven't found a good solution to this yet, the closest thing I have right now is;
http://mpi-forum.org/docs/mpi-2.2/mpi22-report/node83.htm#Node83
and https://blogs.cisco.com/performance/how-to-send-cxx-stl-objects-in-mpi
Please provide some suggestion. Thanks.
Sending non-trivially-copyable objects over MPI is just the same as sending them over any other byte transport: you have to serialize. You can use stringstream to hold the buffer on either end, if it helps.
However, it’s very likely that you shouldn’t do this at all. The data needed to create your objects (e.g., loop bounds and initial values) is probably much smaller and simpler than the form used for ongoing computation. Send that instead, and you can create your complicated objects in parallel as well as reducing communication. (If the parameters are known statically, you don’t have to send anything: each process can just start working on the known initialization.)
I have a big problem..I'm beginner with programming and I try to make a program in C++ for a football league ranking which have to sort the teams depending on their points.
Can someone help with an idea, please?
I created a struct for the teams with the name and the number of points.
How can I sort the teams?P.S. Sorry for my bad English.
This is my code:
#include <iostream>
#include <algorithm>
using namespace std;
//I created a struct for the team.
struct team
{
char name;
int pct;
}v[20];
int main()
{ int i,sw,aux;
for(i=1;i<=4;i++)//read the names
{
cout<<"Team "<<i<<endl;
cin>>v[i].name;
}
for(i=1;i<=4;i++)//get the points
{
cout<<"Team "<<v[i].name<<" points"<<endl;
cin>>v[i].pct;
}
//bubble sort(not working)
do
{
sw=0;
for(i=1;i<=4;i++)
{
if(v[i].pct<v[i+1].pct)
aux=v[i].pct;
v[i].pct=v[i+1].pct;
v[i+1].pct=aux;
sw=1;
}
}while(sw==1);
for(i=1;i<=4;i++)
{
cout<<v[i].pct<<endl;
}
return 0;
}
You need to modify your sort part like this. Assuming you are sorting in desc order.
do
{
sw=0;
for(i=1;i<4;i++) //< not <= ,because in case of the last element you wont have any other element after it to compare
{
if(v[i].pct<v[i+1].pct) // use curly brace as you want all 4 following lines to be executed when its true
{
aux=v[i]; //swap entire struct not just one variable
v[i]=v[i+1];
v[i+1]=aux;
sw=1;
}
}
}while(sw==1);
Also you might need to edit variable type of team name as it can be string.
As you are using C++ there is a one liner function that you can use to sort
//#include<algorithm>
//define comparator function
bool cmp(team a, team b)
{
return a.pct < b.pct;
}
sort(v+1,v+4+1,cmp);
Also you can simply write the comparator inside the struct and then use the sort function:
struct team
{
char name;
int pct;
bool operator<(team other) const
{
return pct > other.pct;
}
}v[20];
sort(v+1,v+4+1);
I'm curious about why you include algorithm but do not use any of it. Do you know STL? Since you include algorithm, I guess you may know some simple functions such as swap, sort and copy. They are easy to use, you just need to type one line instead of writing a bubble sort by yourself. Before you use the sort function, you should define which order can take effect on these teams. Just like this:
bool compareTeams(const Team &t1, const Team &t2) {
if (t1.getScore() == t2.getScore()) {
return t1.getName() < t2.getName();
}
else {
return t1.getScore() < t2.getScore();
}
}
The code above defines a direction we consider to sort the teams, first we sort them by scores, if both of the scores are equal, then we sort them by their names.
Finally We can use the sort function which is ready-made in STL. Now the order we defined can be used. (I guess the array v[] stands for the teams. Am I right?)
std::sort(v, v + 20, compareTeams);
I'm trying to understand how I should implement an associative array which gives constant time for search operations, right now my implementation looks like this:
#include <iostream>
#include <vector>
#include <string>
using namespace std;
template <class Key, class Value> class Dict {
private:
typedef struct Item {
Value value;
Key key;
} Item;
vector<Item> _data;
public:
void clear() {
_data.clear();
}
long size() {
return _data.size();
}
bool is_item(Key key) {
for (int i = 0; i < size(); i++) {
if (_data[i].key == key) return true;
}
return false;
}
bool add_item(Key key, Value value) {
if (is_item(key)) return false;
Item new_item;
new_item.key = key;
new_item.value = value;
_data.push_back(new_item);
return true;
}
Value &operator[](Key key) {
for (int i = 0; i < size(); i++) {
if (_data[i].key == key) return _data[i].value;
}
long idx = size();
Item new_item;
new_item.key = key;
_data.push_back(new_item);
return _data[idx].value;
}
Key get_key(long index) {
if (index < 0) index = 0;
for (int i = 0; i < size(); i++)
if (i == index) return _data[i].key;
return NULL;
}
Value &operator[](long index) {
if (index < 0) index = 0;
for (int i = 0; i < size(); i++) {
if (i == index) return _data[i].value;
}
return _data[0].value;
}
};
A simple test for this:
class Foo {
public:
Foo(int value) {
_value = value;
}
int get_value() {
return _value;
}
void set_value(int value) {
_value = value;
}
private:
int _value;
};
template <class Key, class Value> void print_dict(Dict<Key, Value> &dct) {
if (!dct.size()) {
printf("Empty Dict");
}
for (int i = 0; i < dct.size(); i++) {
printf("%d%s", dct[dct.get_key(i)], i == dct.size() - 1 ? "" : ", ");
}
printf("\n");
}
int main(int argc, char *argv[]) {
printf("\nDict tests\n------------\n");
Dict<string, int> dct;
string key1("key1");
string key2("key2");
string key3("key3");
dct["key1"] = 100;
dct["key2"] = 200;
dct["key3"] = 300;
printf("%d %d %d\n", dct["key1"], dct["key2"], dct["key3"]);
printf("%d %d %d\n", dct[key1], dct[key2], dct[key3]);
print_dict(dct);
dct.clear();
print_dict(dct);
Dict<Foo *, int> dct2;
Foo *f1 = new Foo(100);
Foo *f2 = new Foo(200);
dct2[f1] = 101;
dct2[f2] = 202;
print_dict(dct2);
}
Here's the thing, right now the search operation is linear time and I'd like it to become constant time and I'm wondering about a simple/lightweight way to achieve this.
I've seen hashtables are a possible option but I'd prefer not having to implement a hash function per object. Maybe something similar to an unordered_map... dunno.
Could anyone give some ideas or maybe providing a simple lightweight implementation of what I'm trying to achieve here?
In this fictional example I'm using std::vector to avoid making the question bigger and more complex than what it is but my the real use-case won't be using the STL at all (ie: i'll be coding my own custom implementation of std::vector)
CONSTRAINTS
The reason of not using the STL at all is not because that implementation is not good (fast,generic,full-featured) enough but more because is quite heavy for my size-constrained projects (final exe <=65536bytes). Even this small implementation of the STL is actually quite big to be used as it is
I don't need a full implementation of an associative array but just providing the interface i've already implemented above (main problem being the linear-time search)
I don't care about inserting/deleting methods being slow but definitely I'd like the search/lookup being near to constant time
I guess I'd need to convert the above implementation in an associative array using a hash table but I'm unsure about the relevant implementation details (which hash functions per object, which table size, ...)
Let me address some issues you've raised in your question.
Here's the thing, right now the search operation is linear time and I'd like it to become constant time and I'm wondering about a simple/lightweight way to achieve this.
A simple lightweight way to achieve this, i.e., to have an associative array (a.k.a. key-value-store), is to use one provided by the standard library.
You are coding in a recent version of C++, you are in the lucky position that the standard library actually provides one that satisfies your constant-time requirements:
http://en.cppreference.com/w/cpp/container/unordered_map
The implementation of the data structures shipped as part of a standard library of any decent compiler these days, are probably better than anything you could come up with. (Or why did you ask for give me the code?).
I've seen hashtables are a possible option but I'd prefer not having to implement a hash function per object. Maybe something similar to an unordered_map... dunno.
A std::unordered_map actually is a hash table, and as you can see in the docs, it takes a hash function. As you can see written in the docs there are lots of specializations for lots of types already available, that can help you derive a custom hash function for your custom object types:
http://en.cppreference.com/w/cpp/utility/hash
Could anyone give some ideas or maybe providing a simple lightweight implementation of what I'm trying to achieve here?
Just have a look at the example code to std::unordered_map to see how it's used. If you worry about performance, don't forget to measure. If you really want to consume some input on implementation of hash tables, I liked these talks on the Python dictionary:
https://www.youtube.com/watch?v=C4Kc8xzcA68
https://www.youtube.com/watch?v=p33CVV29OG8
Also have a look at the wikipedia page (if you haven't already):
https://en.wikipedia.org/wiki/Associative_array
In this fictional example I'm using std::vector to avoid making the question bigger and more complex than what it is but my the real use-case won't be using the STL at all (ie: i'll be coding my own custom implementation of std::vector)
Unless you are doing this for educational/recreational purposes, don't do it. Don't be ashamed to base your endeavours on the shoulders of giants. That the standard library wasn't invented in your project is not a problem.
If you want to keep code size small, you should avoid templates as much as possible. At least templates that create non-trivial amounts of code.
For your hash map, that means: stick to one key type and only store void pointers to the values. If you don't want to deal with void* and the casts that go along with it all over in your code, implement one non-template hash map that stores void* as value, with all "no inline" functions. Then create an "all inline" (maybe even all "force inline") wrapper class that uses the void* map internally and just converts T* <-> void*.
If you really really really need different key types, see if you can stick to PODs without padding (memcpy copyable and memcmp comparable). That way you can still use the same hash map class for everything: you just have to tell the map (at runtime) what the key-size is. Then you can copy the keys into the map using memcpy, compare using memcmp and hash them using any hash algorithm that can hash byte sequences (=almost every hash algorithm).
Of course you'll also want to do a lot of other stuff, e.g. avoid inlining any non-trivial functions, avoid C-Runtime library functions, disable exception handling and RTTI etc., but that's a different topic.
Or, maybe just stick to plain C :)
I'm relatively new to programming and I did really well in my introductory class. However, as we are starting to get into the more advanced concepts of C++, I'm becoming more and more lost. I'm having a problem with a lab assignment, I hope you guys can help!
Write a generic list class called GenericList. The class should use a vector and be able to >be created with any type name. The class should have the following members:
A simple constructor
add(item) - add the item to the list
grabSmallest() - find, return and remove the smallest item in the list
Here is what I have so far, I believe it is at least set up correctly:
EDIT
This is what I have after the corrections that have been suggested, I've ran into a different problem now, though. Here is the revised code:
#include <iostream>
#include <vector>
#include <string>
using namespace std;
template<typename T>
class GenericList
{
public:
GenericList();
void add(T value);
T grabSmallest();
private:
vector<T> listVector;
};
template<typename T>
GenericList<T>::GenericList()
{
}
template<typename T>
void GenericList<T>::add(T value)
{
listVector.push_back(value);
}
template<typename T>
T GenericList<T>::grabSmallest()
{
int smallest = listVector[0];
for (int i = 0; i < listVector.size(); i++)
{
if (listVector[i] < smallest)
{
smallest = listVector[i];
}
}
}
int main (){
GenericList<int> myList;
myList.add(10);
myList.add(5);
myList.add(20);
myList.add(15);
for(int i=0;i<4;i++)
cout << myList.grabSmallest() << " ";
}
I'm now having problems with my for loop in the grab function. Apparently, the compiler is putting random numbers into the vector.
Where is the last?
Even you have the last,
template<typename T>
void GenericList<T>::add(const T &value)
{
listVector[last++] = value; // <- should it be last++ or ++last?
}
or do you mean:
template<typename T>
void GenericList<T>::add(const T &value)
{
listVector.push_back(value)
}
BTW, With vector, you dont need the last field. It's kept in the vector: ` vector.size(). But why wrap vector when you could just use vector directly?
if you want the just want the smallest, priority_queue will do.
As gongzhitaao said, that line is not liking you because you never declare last and thus the compiler doesn't know what to do with it. as they said, you need to use push_back to solve that problem.
But you also need to solve another problem: what happens if they don't use int as their type? What if they want the "least" member of a custom class? You need to change this:
vector<int> listVector;
to this
vector<T> listVector;
So that the vector picks up the custom type that the template parameter T is specifying.
For grabSmallest I suggest you use some type of search to determine which element is the smallest, such as picking the first element, then looping through after that to see if each subsequent one is smaller or not. If it is, take that as your value, and loop. If not, just keep going. Whichever is left over at the end is smallest. But remember to use T as your type all the way through. Sorting it on every insert isn't necessary with this method.
As this is homework I didn't want to give you 100% of the answer with code, but hopefully the preceding paragraph is enough to get you going.
Edit: figured it out. Try www.codepad.org and run your code through it.
Basically, two errors in your grabSmallest() method.
It should be T smallest = listVector[0] not int. You should also have a "guard" that returns a default value (or throws an exception) if the list is empty.
grabSmallest() is supposed to return a value, but you forgot to. So your compiler is apparently way too forgiving, and didn't flag that as an error. Put return smallest as the last line of the method, just after the for loop.
This is my first time using this site so sorry for any bad formatting or weird formulations, I'll try my best to conform to the rules on this site but I might do some misstakes in the beginning.
I'm right now working on an implementation of some different bin packing algorithms in C++ using the STL containers. In the current code I still have some logical faults that needs to be fixed but this question is more about the structure of the program. I would wan't some second opinion on how you should structure the program to minimize the number of logical faults and make it as easy to read as possible. In it's current state I just feel that this isn't the best way to do it but I don't really see any other way to write my code right now.
The problem is a dynamic online bin packing problem. It is dynamic in the sense that items have an arbitrary time before they will leave the bin they've been assigned to.
In short my questions are:
How would the structure of a Bin packing algorithm look in C++?
Is STL containers a good tool to make the implementation be able to handle inputs of arbitrary lenght?
How should I handle the containers in a good, easy to read and implement way?
Some thoughts about my own code:
Using classes to make a good distinction between handling the list of the different bins and the list of items in those bins.
Getting the implementation as effective as possible.
Being easy to run with a lot of different data lengths and files for benchmarking.
#include <iostream>
#include <fstream>
#include <list>
#include <queue>
#include <string>
#include <vector>
using namespace std;
struct type_item {
int size;
int life;
bool operator < (const type_item& input)
{
return size < input.size;
}
};
class Class_bin {
double load;
list<type_item> contents;
list<type_item>::iterator i;
public:
Class_bin ();
bool operator < (Class_bin);
bool full (type_item);
void push_bin (type_item);
double check_load ();
void check_dead ();
void print_bin ();
};
Class_bin::Class_bin () {
load=0.0;
}
bool Class_bin::operator < (Class_bin input){
return load < input.load;
}
bool Class_bin::full (type_item input) {
if (load+(1.0/(double) input.size)>1) {
return false;
}
else {
return true;
}
}
void Class_bin::push_bin (type_item input) {
int sum=0;
contents.push_back(input);
for (i=contents.begin(); i!=contents.end(); ++i) {
sum+=i->size;
}
load+=1.0/(double) sum;
}
double Class_bin::check_load () {
return load;
}
void Class_bin::check_dead () {
for (i=contents.begin(); i!=contents.end(); ++i) {
i->life--;
if (i->life==0) {
contents.erase(i);
}
}
}
void Class_bin::print_bin () {
for (i=contents.begin (); i!=contents.end (); ++i) {
cout << i->size << " ";
}
}
class Class_list_of_bins {
list<Class_bin> list_of_bins;
list<Class_bin>::iterator i;
public:
void push_list (type_item);
void sort_list ();
void check_dead ();
void print_list ();
private:
Class_bin new_bin (type_item);
bool comparator (type_item, type_item);
};
Class_bin Class_list_of_bins::new_bin (type_item input) {
Class_bin temp;
temp.push_bin (input);
return temp;
}
void Class_list_of_bins::push_list (type_item input) {
if (list_of_bins.empty ()) {
list_of_bins.push_front (new_bin(input));
return;
}
for (i=list_of_bins.begin (); i!=list_of_bins.end (); ++i) {
if (!i->full (input)) {
i->push_bin (input);
return;
}
}
list_of_bins.push_front (new_bin(input));
}
void Class_list_of_bins::sort_list () {
list_of_bins.sort();
}
void Class_list_of_bins::check_dead () {
for (i=list_of_bins.begin (); i !=list_of_bins.end (); ++i) {
i->check_dead ();
}
}
void Class_list_of_bins::print_list () {
for (i=list_of_bins.begin (); i!=list_of_bins.end (); ++i) {
i->print_bin ();
cout << "\n";
}
}
int main () {
int i, number_of_items;
type_item buffer;
Class_list_of_bins bins;
queue<type_item> input;
string filename;
fstream file;
cout << "Input file name: ";
cin >> filename;
cout << endl;
file.open (filename.c_str(), ios::in);
file >> number_of_items;
for (i=0; i<number_of_items; ++i) {
file >> buffer.size;
file >> buffer.life;
input.push (buffer);
}
file.close ();
while (!input.empty ()) {
buffer=input.front ();
input.pop ();
bins.push_list (buffer);
}
bins.print_list ();
return 0;
}
Note that this is just a snapshot of my code and is not yet running properly
Don't wan't to clutter this with unrelated chatter just want to thank the people who contributed, I will review my code and hopefully be able to structure my programming a bit better
How would the structure of a Bin packing algorithm look in C++?
Well, ideally you would have several bin-packing algorithms, separated into different functions, which differ only by the logic of the algorithm. That algorithm should be largely independent from the representation of your data, so you can change your algorithm with only a single function call.
You can look at what the STL Algorithms have in common. Mainly, they operate on iterators instead of containers, but as I detail below, I wouldn't suggest this for you initially. You should get a feel for what algorithms are available and leverage them in your implementation.
Is STL containers a good tool to make the implementation be able to handle inputs of arbitrary length?
It usually works like this: create a container, fill the container, apply an algorithm to the container.
Judging from the description of your requirements, that is how you'll use this, so I think it'll be fine. There's one important difference between your bin packing algorithm and most STL algorithms.
The STL algorithms are either non-modifying or are inserting elements to a destination. bin-packing, on the other hand, is "here's a list of bins, use them or add a new bin". It's not impossible to do this with iterators, but probably not worth the effort. I'd start by operating on the container, get a working program, back it up, then see if you can make it work for only iterators.
How should I handle the containers in a good, easy to read and implement way?
I'd take this approach, characterize your inputs and outputs:
Input: Collection of items, arbitrary length, arbitrary order.
Output: Collection of bins determined by algorithm. Each bin contains a collection of items.
Then I'd worry about "what does my algorithm need to do?"
Constantly check bins for "does this item fit?"
Your Class_bin is a good encapsulation of what is needed.
Avoid cluttering your code with unrelated stuff like "print()" - use non-member help functions.
type_item
struct type_item {
int size;
int life;
bool operator < (const type_item& input)
{
return size < input.size;
}
};
It's unclear what life (or death) is used for. I can't imagine that concept being relevant to implementing a bin-packing algorithm. Maybe it should be left out?
This is personal preference, but I don't like giving operator< to my objects. Objects are usually non-trivial and have many meanings of less-than. For example, one algorithm might want all the alive items sorted before the dead items. I typically wrap that in another struct for clarity:
struct type_item {
int size;
int life;
struct SizeIsLess {
// Note this becomes a function object, which makes it easy to use with
// STL algorithms.
bool operator() (const type_item& lhs, const type_item& rhs)
{
return lhs.size < rhs.size;
}
}
};
vector<type_item> items;
std::sort(items.begin, items.end(), type_item::SizeIsLess);
Class_bin
class Class_bin {
double load;
list<type_item> contents;
list<type_item>::iterator i;
public:
Class_bin ();
bool operator < (Class_bin);
bool full (type_item);
void push_bin (type_item);
double check_load ();
void check_dead ();
void print_bin ();
};
I would skip the Class_ prefix on all your types - it's just a bit excessive, and it should be clear from the code. (This is a variant of hungarian notation. Programmers tend to be hostile towards it.)
You should not have a class member i (the iterator). It's not part of class state. If you need it in all the members, that's ok, just redeclare it there. If it's too long to type, use a typedef.
It's difficult to quantify "bin1 is less than bin2", so I'd suggest removing the operator<.
bool full(type_item) is a little misleading. I'd probably use bool can_hold(type_item). To me, bool full() would return true if there is zero space remaining.
check_load() would seem more clearly named load().
Again, it's unclear what check_dead() is supposed to accomplish.
I think you can remove print_bin and write that as a non-member function, to keep your objects cleaner.
Some people on StackOverflow would shoot me, but I'd consider just making this a struct, and leaving load and item list public. It doesn't seem like you care much about encapsulation here (you're only need to create this object so you don't need do recalculate load each time).
Class_list_of_bins
class Class_list_of_bins {
list<Class_bin> list_of_bins;
list<Class_bin>::iterator i;
public:
void push_list (type_item);
void sort_list ();
void check_dead ();
void print_list ();
private:
Class_bin new_bin (type_item);
bool comparator (type_item, type_item);
};
I think you can do without this class entirely.
Conceptually, it represents a container, so just use an STL container. You can implement the methods as non-member functions. Note that sort_list can be replaced with std::sort.
comparator is too generic a name, it gives no indication of what it compares or why, so consider being more clear.
Overall Comments
Overall, I think the classes you've picked adequately model the space you're trying to represent, so you'll be fine.
I might structure my project like this:
struct bin {
double load; // sum of item sizes.
std::list<type_item> items;
bin() : load(0) { }
};
// Returns true if the bin can fit the item passed to the constructor.
struct bin_can_fit {
bin_can_fit(type_item &item) : item_(item) { }
bool operator()(const bin &b) {
return item_.size < b.free_space;
}
private:
type_item item_;
};
// ItemIter is an iterator over the items.
// BinOutputIter is an output iterator we can use to put bins.
template <ItemIter, BinOutputIter>
void bin_pack_first_fit(ItemIter curr, ItemIter end, BinOutputIter output_bins) {
std::vector<bin> bins; // Create a local bin container, to simplify life.
for (; curr != end; ++curr) {
// Use a helper predicate to check whether the bin can fit this item.
// This is untested, but just for an idea.
std::vector<bin>::iterator bin_it =
std::find_if(bins.begin(), bins.end(), bin_can_fit(*curr));
if (bin_it == bins.end()) {
// Did not find a bin with enough space, add a new bin.
bins.push_back(bin);
// push_back invalidates iterators, so reassign bin_it to the last item.
bin_it = std::advance(bins.begin(), bins.size() - 1);
}
// bin_it now points to the bin to put the item in.
bin_it->items.push_back(*curr);
bin_it->load += curr.size();
}
std::copy(bins.begin(), bins.end(), output_bins); // Apply our bins to the destination.
}
void main(int argc, char** argv) {
std::vector<type_item> items;
// ... fill items
std::vector<bin> bins;
bin_pack_first_fit(items.begin(), items.end(), std::back_inserter(bins));
}
Some thoughts:
Your names are kinda messed up in places.
You have a lot of parameters named input, thats just meaningless
I'd expect full() to check whether it is full, not whether it can fit something else
I don't think push_bin pushes a bin
check_dead modifies the object (I'd expect something named check_*, to just tell me something about the object)
Don't put things like Class and type in the names of classes and types.
class_list_of_bins seems to describe what's inside rather then what the object is.
push_list doesn't push a list
Don't append stuff like _list to every method in a list class, if its a list object, we already know its a list method
I'm confused given the parameters of life and load as to what you are doing. The bin packing problem I'm familiar with just has sizes. I'm guessing that overtime some of the objects are taken out of bins and thus go away?
Some further thoughts on your classes
Class_list_of_bins is exposing too much of itself to the outside world. Why would the outside world want to check_dead or sort_list? That's nobodies business but the object itself. The public method you should have on that class really should be something like
* Add an item to the collection of bins
* Print solution
* Step one timestep into the future
list<Class_bin>::iterator i;
Bad, bad, bad! Don't put member variables on your unless they are actually member states. You should define that iterator where it is used. If you want to save some typing add this: typedef list::iterator bin_iterator and then you use bin_iterator as the type instead.
EXPANDED ANSWER
Here is my psuedocode:
class Item
{
Item(Istream & input)
{
read input description of item
}
double size_needed() { return actual size required (out of 1) for this item)
bool alive() { return true if object is still alive}
void do_timestep() { decrement life }
void print() { print something }
}
class Bin
{
vector of Items
double remaining_space
bool can_add(Item item) { return true if we have enough space}
void add(Item item) {add item to vector of items, update remaining space}
void do_timestep() {call do_timestep() and all Items, remove all items which indicate they are dead, updating remaining_space as you go}
void print { print all the contents }
}
class BinCollection
{
void do_timestep { call do_timestep on all of the bins }
void add(item item) { find first bin for which can_add return true, then add it, create a new bin if neccessary }
void print() { print all the bins }
}
Some quick notes:
In your code, you converted the int size to a float repeatedly, that's not a good idea. In my design that is localized to one place
You'll note that the logic relating to a single item is now contained inside the item itself. Other objects only can see whats important to them, size_required and whether the object is still alive
I've not included anything about sorting stuff because I'm not clear what that is for in a first-fit algorithm.
This interview gives some great insight into the rationale behind the STL. This may give you some inspiration on how to implement your algorithms the STL-way.