#include <iostream>
#include <vector>
#include <string>
#include <math.h>
using namespace std;
struct Node{
string data;
Node* next;
Node(){
data = "";
next = NULL;
}
};
int computeHash(string s, int m){
int p = 1000000007;
int x = 263;
unsigned long long sum = 0;
unsigned long long val = 0;
for(int i = 0; i < s.length(); i++){
val = pow(x, i);
sum = (sum + s[i] * val) % p;
}
sum = sum % m;
return sum;
}
int main(){
int buckets;
cin >> buckets;
int n;
cin >> n;
string tag;
string s;
vector< vector<string> > myStore(n);
for(int i = 0; i < n; i++){
cin >> s;
myStore.at(i).push_back(s);
cin >> tag;
myStore.at(i).push_back(tag);
}
Node** arr= new Node*[buckets];
for(int i = 0; i < n; i++){
if(!myStore[i][0].compare("add")){
s = myStore[i][1];
int hash = computeHash(s,buckets);
cout << hash << endl;
}
}
return 0;
}
I am trying to write a program to implement hashing with chains. I am trying to create an array of nodes so that I can append if two strings have the same hash value.
But I am having a problem with the initialization of array of Nodes. I thought the nodes in the array would be pointing to NULL. But when I tried to debug in gdb it is showing some other thing.
Can someone explain where I am wrong on comment about this behavior. Why arr1 and arr[2] are pointing to some memory location instead of null. I also tried to remove the default constructor but still getting the same results. Any help would be appreciated.
You're allocating an array of pointers. Pointers don't have constructors, or default initialization; you're getting random memory (from the allocation).
If you want the array to be NULL-ed out, you need to do so yourself (eg: memcpy, etc.).
You have initialized vector of size n of vectors of size 0 of strings.
Then you want to get the '[1]' (the second element of empty vector of strings)
You have to inutialize them separately.
e.g. in "for" cycle.
Updated. Use myStore.at(i).at(1) instead of myStore[i][1] to achieve checking of boundary conditions. (Try it, you will understand that the problem with vector indeed)
Related
As I'm new to c++ I get runtime error for first example(I mean I tested my program with 5 examples it actually happens automatically by a site for testing) of my program I know that's because of exceeding time for running it but I dunno how to fix this.
My program get n numbers from user and finds the largest one and prints it.
#include<iostream>
#include<curses.h>
using namespace std;
int main()
{
int n;
cin >> n;
int *p = new int(n);
for(int i = 1; i<=n; i++){
cin >> *(p+i);
}
int largest = *p;
for(int i = 1; i<=n; i++){
if(largest < *(p+i))
largest = *(p+i);
}
cout << largest;
return(0);
}
int *p=new int(n);
The line above allocates just a single int, and sets the value to n. It does not allocate an array of n integers.
That line should be:
int *p=new int[n];
And then delete [] p; to deallocate the memory.
But better yet:
#include <vector>
//...
std::vector<int> p(n);
is the preferred way to utilize dynamic arrays in C++.
Then the input loop would simply be:
for(int i=0;i<n; i++)
{
cin >> p[i];
}
That same input loop could have been used if you had used the pointer version.
Then you have this error:
for(int i=1;i<=n;i++)
Arrays (and vectors) are indexed starting from 0 with the upper index at n-1, where n is the total number of elements. That loop has an off-by-one error, where it exceeds the upper index on the last loop.
Basically any loop that uses <= as the limiting condition is suspect. That line should be:
for(int i=0; i<n; i++)
(Note that I changed the code above to fix this error).
However ultimately, that entire loop to figure out the largest can be accomplished with a single line of code using the std::max_element function:
#include <algorithm>
//...
int largest = *std::max_element(p, p + n);
and if using std::vector:
#include <algorithm>
//...
int largest = *std::max_element(p.begin(), p.begin() + n);
I've commented on suggested changes in this slightly modified version:
#include <iostream>
int main()
{
unsigned n; // don't allow a negative amount of numbers
if(std::cin >> n) { // check that "cin >> n" succeeds
int* p=new int[n]; // allocate an array of n ints instead of one int with value n
for(int i=0; i < n; ++i) { // corrected bounds [0,n)
if(not (std::cin >> p[i])) return 1; // check that "cin >> ..." succeeds
}
int largest = p[0];
for(int i=1; i < n; ++i) { // corrected bounds again, [1,n)
if(largest < p[i])
largest = p[i];
}
delete[] p; // free the memory when done
std::cout << largest << '\n';
}
}
Note that using *(p + i) does the same as using p[i]. The latter is often preferred.
This would work if all cin >> ... works, but shows some of the hazards when using raw pointers. If extracting the n ints failes, the program will return 1 and leak the memory allocated with new int[n].
A rewrite using a smart pointer (std::unique_ptr<int[]>) that automatically deallocates the memory when it goes out of scope:
#include <iostream>
#include <memory> // std::unique_ptr
int main()
{
unsigned n;
if(std::cin >> n) {
std::unique_ptr<int[]> p(new int[n]);
for(int i=0; i < n; ++i) { // corrected bounds [0,n)
if(not (std::cin >> p[i])) return 1; // will not leak "p"
}
int largest = p[0];
for(int i=1; i < n; ++i) {
if(largest < p[i])
largest = p[i];
}
std::cout << largest << '\n';
} // p is automatically delete[]ed here
}
However, it's often convenient to store an array and its size together and to do this, you could use a std::vector<int> instead. It comes with a lot of convenient member functions, like, size() - and also begin() and end() which lets you use it in range-based for loops.
#include <iostream>
#include <vector> // std::vector
int main()
{
unsigned n;
if(std::cin >> n) {
std::vector<int> p(n); // a vector of n ints
// a range-based for loop, "elem" becomes a refrence to each element in "p":
for(int& elem : p) {
if(not (std::cin >> elem)) return 1;
}
int largest = p[0];
for(int i = 1; i < p.size(); ++i) { // using the size() member function
if(largest < p[i])
largest = p[i];
}
std::cout << largest << '\n';
}
}
That said, you don't need to store any number in an array to figure out what the largest number is. Instead, just compare the input with the currently largest number.
#include <iostream>
#include <limits> // std::numeric_limits
int main()
{
unsigned n;
if(std::cin >> n) {
// initialize with the smallest possible int:
int largest = std::numeric_limits<int>::min();
while(n--) {
int tmp;
if(not (std::cin >> tmp)) return 1;
if(largest < tmp)
largest = tmp;
}
std::cout << largest << '\n';
}
}
I was trying to solve this question
but codechef.com says the answer is wrong.
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
int t, n, diff, mindiff;
cin >> t;
cin >> n;
int val[n];
while(t--)
{
mindiff = 1000000000;
for(int i = 0; i<n; i++)
{
cin >> val[i];
}
int a = 0;
for(a = 0; a<n ; a++)
{
for(int b=a+1; b<n ; b++)
{
diff = abs(val[a] - val[b]);
if(diff <= mindiff)
{
mindiff = diff;
}
}
}
cout << mindiff << endl;
}
return 0;
}
The results are as expected (for at least the tests I did) buts the website says its wrong.
There are a few things in your code that you should change:
Use std::vector<int> and not variable-length arrays (VLA's):
Reasons:
Variable length arrays are not standard C++. A std::vector is standard C++.
Variable length arrays may exhaust stack memory if the number of entries is large. A std::vector gets its memory from the heap, not the stack.
Variable length arrays suffer from the same problem as regular arrays -- going beyond the bounds of the array leads to undefined
behavior. A std::array has an at() function that can check boundary access when desired.
Use the maximum int to get the maximum integer value.
Instead of
mindif = 1000000000;
it should be:
#include <climits>
//...
int mindiff = std::numeric_limits<int>::max();
As to the solution you chose, the comments in the main section about the nested loop should be addressed.
Instead of a nested for loop, you should sort the data first. Thus finding the minimum value between two values is much easier and with less time complexity.
The program can look something like this (using the data provided at the link):
#include <iostream>
#include <vector>
#include <climits>
#include <algorithm>
int main()
{
int n = 5;
std::vector<int> val = {4, 9, 1, 32, 13};
int mindiff = std::numeric_limits<int>::max();
std::sort(val.begin(), val.end());
for(int a = 0; a < n-1 ; a++)
mindiff = std::min(val[a+1] - val[a], mindiff);
std::cout << mindiff;
}
Output:
3
To do this you can use a simple for():
// you already have an array called "arr" which contains some numbers.
int biggestNumber = 0;
for (int i = 0; i < arr.size(); i++) {
if (arr[i] > biggestNumber) {
biggestNumber = arr[i];
}
}
arr.size will get the array's length so that you can check every value from the position 0 to the last one which is arr.size() - 1 (because arrays are 0 based in c++).
Hope this helps.
I want to enter n times values for c and e arrays. The following program doesn't allow me to even enter the value of 'n'. Could you tell me where is the mistake?
#include <iostream>
using namespace std;
int main()
{
int n,c[n],e[n];
cin>>n;
for(int i=0;i<n;i++){
cin>>c[i]>>e[i];
}
return 0;
}
"n" should be defined before using it to fix array size. Also, const int or constant should be used to declare array size not plain int.
In order to use plain datatype, you can initialize array dynamically like
vector<int> a(n); or
int a = new int[n]
int n,c[n],e[n];
This declaration creates arrays c and e on stack with random size, because n as an automatic variable is initialized with random value. Instead you need to dynamically create arrays on heap or use std::vector.
Example:
#include <iostream>
#include <vector>
using namespace std;
int main() {
// your code goes here
int n;
vector<int> v;
std::cin >> n;
v.resize( n);
for( int i = 0; i < n; ++i) {
cin >> v[i];
}
for( int i = 0; i < n; ++i) {
cout << v[i];
}
return 0;
}
http://ideone.com/QhgfNv
In the line of
int n,c[n],e[n];
Computer don't know the exact value of 'n', so it can't alloc memory of array.
The simplest solution is create array with fixed number, and check n after you know the value of n as follows:
int n, c[1024], e[1024];
cin >> n;
if (n > 1024) { /* error */ }
The other way is malloc memory after u know the value of n:
int n;
cin >> n;
int *c = new int[n];
int *e = new int[n];
xxxx
delete [] c;
delete [] e;
You can try something like this:
#include <iostream>
using namespace std;
int main()
{
int temp = 100; /*Random value*/
int c[temp];
int e[temp];
int n;
cin>>n;
for(int i=0;i<n;i++){
cin>>c[i]>>e[i];
}
return 0;
}
Now, I chose temp as 100, but you can do big as your int can store. Now, if n is lower than temp, your for cycle will let you save your values without troubles.
I want to use the code below and I want to use it for "unknown size of input". For example there is an array int cac[1000][1000]. I can use vector<vector<int> > array;, then how can i initialize it with -1 ? Any suggestions?
#include <sstream>
#include <iostream>
#include <vector>
#include <cstdlib>
#include <memory.h>
using namespace std;
int cac[1000][1000];
string res[1000][1000];
vector<string> words;
int M;
int go(int a, int b){
if(cac[a][b]>= 0) return cac[a][b];
if(a == b) return 0;
int csum = -1;
for(int i=a; i<b; ++i){
csum += words[i].size() + 1;
}
if(csum <= M || a == b-1){
string sep = "";
for(int i=a; i<b; ++i){
res[a][b].append(sep);
res[a][b].append(words[i]);
sep = " ";
}
return cac[a][b] = (M-csum)*(M-csum);
}
int ret = 1000000000;
int best_sp = -1;
for(int sp=a+1; sp<b; ++sp){
int cur = go(a, sp) + go(sp,b);
if(cur <= ret){
ret = cur;
best_sp = sp;
}
}
res[a][b] = res[a][best_sp] + "\n" + res[best_sp][b];
return cac[a][b] = ret;
}
int main(int argc, char ** argv){
memset(cac, -1, sizeof(cac));
M = atoi(argv[1]);
string word;
while(cin >> word) words.push_back(word);
go(0, words.size());
cout << res[0][words.size()] << endl;
}
What you can do is to use a associative array, where the key is a pair (rowPosition, ColumnPosition). When you want to set array[i][j] you just add or update the value assoArray[Pair(i,j)]. You can assume that any element which is not in the associative array has the initial value.
In general infinite multidimensional arrays are used for theoretical purpose.I hope i didn't misunderstood the question.
Using std::vector from the STL is much more straightforward than the following solution, which was pointed out in the comments for this post. I find that this site explains that topic effectively: http://www.learncpp.com/cpp-programming/16-2-stl-containers-overview/
An array of infinite size is not actually possible. However, you can achieve basically that effect using dynamic allocation. Here's some sample code:
int counter = 0;
int* myArray = new int[1000];
Fill the array with data, incrementing counter each time you add a value. When counter reaches 1000, do the following:
int* largerArray = new int[2000];
for( int i = 0; i < 1000; i++ )
{
largerArray[i] = myArray[i];
}
delete[] myArray;
myArray = largerArray;
With this method, you create the closest thing possible to an infinitely sized array, and I don't believe performance will be an issue with the copy piece
I am getting a crash error at run time and not sure what exactly to do with the function or how to get the data for it.
FUNCTION DETAILS
Write a function that accepts an int array and size as arguments, then create a new array that is one element bigger than the given. Setting the first element to 0, then copying over what is in the argument array to the new array.
MAIN DETAILS
Use in a program reading int n from input, then read int n from file data name data
passing it to element shifter, then printing it to output (one per line).
#include <cstdlib>
#include <iostream>
#include <fstream>
using namespace std;
int element_shift(int elmts[], int size) {
int new_size = size + 1;
int shifter[new_size];
int *elmt_sft;
shifter[0] = 0;
for (int i = 1; i >= new_size; i++) {
shifter[i + 1] = elmts[i];
}
return *elmt_sft;
}
int main() {
fstream infile;
infile.open("D:\\data.txt");
int n, x;
infile >> x;
cout << "size of array: ";
cin >> n;
const int ARRAY_SIZE = n + x;
int elements[ARRAY_SIZE];
element_shift(elements, ARRAY_SIZE);
system("PAUSE");
return EXIT_SUCCESS;
}
First of all ARRAY_SIZE declared in the main function is not a constant variable but defined at run-time depending on user inputs. This means that the array elements should be created dynamically. On the other hand you read some x variable which is only used to define the size of the array and didn't initialized the array at all. I guess that the problem statement is to read the size of the array from the input, then the data of the array from the file.
There are also lot of mistakes in element_shift function.
Your code should look like something similar to this:
#include <cstdlib>
#include <iostream>
#include <fstream>
using namespace std;
void element_shift(int* elmts, int size)
{
int new_size = size + 1;
int* shifter = new int[new_size];
shifter[0] = 0;
for(int i = 0; i < size; ++i)
{
shifter[i + 1] = elmts[i];
}
delete [] elmts;
elmts = shifter;
}
int main()
{
fstream infile;
infile.open("D:\\data.txt");
int n;
cout << "size of array: ";
cin >> n;
int* elements = new int[n];
for (int i = 0; i < n; ++i) {
infile >> elements[i];
}
element_shift(elements, n);
for (int i = 0; i < n; ++i) {
std::cout << elements[i] << std::endl;
}
return EXIT_SUCCESS;
}
First off, you spend alot of time creating the shifted array but don't return it back.
int element_shift(int elmts[], int size) {
int new_size = size + 1;
int shifter[new_size];
int *elmt_sft;
shifter[0] = 0;
for (int i = 1; i >= new_size; i++) {
shifter[i + 1] = elmts[i];
}
return *elmt_sft;
}
The elmt_sft pointer is never assigned. You are trying to access memory that is not there by using *elmt_sft. This may be causing your error. Also this function has no way of returning the new array shifter because that variable is locally declared and will disappear once the function exits. If you want to create something new in the function and still have it in memory once the function exits, I recommend creating the array dynamically and returning a pointer to it.
This is untested but should start you in the right direction. It will return a separate dynamically allocated array that will not override your other one.
int* element_shift(int elmts[], int size) {
int *result_array = new int[size + 1]; //dynamically create new array MAKE SURE TO DELETE
result_array[0] = 0; //set 0 index to 0
for (int i = 1; i < size + 1; i++)//start at 1 of the result and put value in
{
result_array[i] = elmts[i - 1];
}
return result_array; //returning pointer
}