Copying elements from one array to another c++ - c++

I have looked and looked and am still lost on how to copy or get elements from an array and put them into new arrays ( divide and conquer is the goal).
I have an array that generates 100 random numbers. I need to split the random numbers into 4 smaller arrays obviously containing 25 elements and not have any duplicates. I have read about using pointers, but honestly I don't understand why even use a pointer. Why do I care about another variables address?
I don't know how to do this. Here is my code so far:
#include <iostream>
#include <time.h>
#include <stdlib.h>
using namespace std;
int main()
{
// Seed the random number generator
srand(time(NULL));
//create an array to store our random numbers in
int Orignumbers[100] = {};
// Arrays for the divide and conquer method
int NumbersA [25] = {};
int NumbersB [25] = {};
int NumbersC [25] = {};
int NumbersD [25] = {};
//Generate the random numbers
for(int i =0; i < 100; i++)
{
int SomeRandomNumber = rand() % 100 + 1;
// Throw random number into the array
Orignumbers[i] = SomeRandomNumber;
}
// for(int i = 0; i < ) started the for loop for the other arrays, this is where I am stuck!!
// Print out the random numbers
for(int i = 0; i < 100; i++)
{
cout << Orignumbers[i] << " , ";
}
}

"divide and conquer" is rather easy; when copying into NumbersA and so forth, you just have to access your Originnumbers with a proper offset, i.e. 0, 25, 50, and 75:
for(int i = 0; i < 25; i++) {
NumbersA[i] = Orignumbers[i];
NumbersB[i] = Orignumbers[i+25];
NumbersC[i] = Orignumbers[i+50];
NumbersD[i] = Orignumbers[i+75];
}
The thing about "no duplicates" is a little bit more tricky. Generating a random sequence of unique numbers is usually solved through "shuffling". Standard library provides functions for that:
#include <random>
#include <algorithm>
#include <iterator>
#include <vector>
int main()
{
std::random_device rd;
std::mt19937 g(rd());
int Orignumbers[100];
//Generate the random numbers without duplicates
for(int i =0; i < 100; i++) {
Orignumbers[i] = i+1;
}
std::shuffle(Orignumbers, Orignumbers+100, g);
// Arrays for the divide and conquer method
int NumbersA [25] = {};
int NumbersB [25] = {};
int NumbersC [25] = {};
int NumbersD [25] = {};
for(int i = 0; i < 25; i++) {
NumbersA[i] = Orignumbers[i];
NumbersB[i] = Orignumbers[i+25];
NumbersC[i] = Orignumbers[i+50];
NumbersD[i] = Orignumbers[i+75];
}
// Print out the random numbers
for(int i = 0; i < 100; i++)
{
cout << Orignumbers[i] << " , ";
}
}

Problem:
The program can't be guaranteed to have no duplicate value as the rand() function can generate any random sequence and that may include the decimal value of 99 for 99 times though probability is very low but chances are.
Example:
for(loop=0; loop<9; loop++)
printf("%d", Rand()%10);
If looped for 10 times, it may result some values like:
Output: 6,1,1,1,2,9,1,3,6,9
Compiled Successfully:
Hence, no certainity that values won't repeat
Possibly Solution:
There could be a solution where you can place the values in OriginalArray and compare the rand() generate values against the OriginalArray values.
For first iteration of loop, you can directly assign value to OriginalArray then from 2nd iteration of loop you've to compare rand() value against OriginalArray but insertion time consumption may be higher than O(NN) as rand() function may repeat values.
Possibly Solution:
#include <iostream>
#include <time.h>
#include <stdlib.h>
using namespace std;
int main()
{
int Orignumbers[100] ;
int NumbersA [25] ,
NumbersB [25] ,
NumbersC [25] ,
NumbersD [25] ;
srand(time(NULL));
for(int i =0; i < 100; i++){
Orignumbers[i] = rand() % 100+1;
for(int loop=0; loop<i; loop++) {
if(Orignumber[loop] == Orignumber[i] ) {
i--;
break;
}
}
}
//Placing in four different arrays thats maybe needed.
for(int i = 0; i <25; i++ ) {
NumbersA[i] = Orignumbers[i];
NumbersB[i] = Orignumbers[i+25];
NumbersC[i] = Orignumbers[i+50];
NumbersD[i] = Orignumbers[i+75];
}
for(int i = 0; i < 99; i++)
cout << Orignumbers[i] << " , ";
}

As you tagged your question with C++ then forget about old-fashion arrays, let's do it C++ style.
You want to split your array into 4 arrays and they should not have duplicate numbers, so you can't have a number 5 times in your original array, because then surely one of your 4 arrays will have a duplicate one, So here is the way I propose to do it :
#include <set>
#include <ctime>
#include <vector>
int main() {
std::multiset<int> allNums;
std::srand(unsigned(std::time(0)));
for (int i = 0; i < 100; ++i) {
int SomeRandomNumber = std::rand() % 100 + 1;
if (allNums.count(SomeRandomNumber) < 4) {
allNums.insert(SomeRandomNumber);
}
else {
--i;
}
}
std::vector<int> vOne, vTwo, vThree, vFour;
for (auto iter = allNums.begin(); iter != allNums.end(); ++iter) {
vOne.push_back(*iter);
++iter;
vTwo.push_back(*iter);
++iter;
vThree.push_back(*iter);
++iter;
vFour.push_back(*iter);
}
system("pause");
return 0;
}
EDIT : As you mentioned in the comments, you just want to find a number in an array, so how about this :
for (int i = 0; i < 100; ++i) {
if (origArray[i] == magicNumber) {
cout << "magicNumber founded in index " << i << "of origArray";
}
}

On some situations, even on C++, the use of arrays might be preferable than vectors, for example, when dealing with multidimensional arrays (2D, 3D, etc) that needs to be continuous and ordered on the memory. (e.g. later access by other applications or faster exporting to file using formats such as HDF5.)
Like Jesper pointed out, you may use Copy and I would add MemCopy to copy the content of an array or memory block into another.
Don't underestimate the importance of pointers, they may solve your problem without the need doing any copy. A bit like Stephan solution but without the need of the index variable "i", just having the pointers initialized at different places on the array. For a very large number of elements, such strategy will save some relevant processing time.

Related

How to find the minimun of an array?

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.

How to avoid using same members in a matrix which is made by rand() function?

I'm trying to make a 5x10 matrix with full of random letters and once the letter is used, it shouldn't be used again. 25 of them have to be small letters, 25 ought to be big letters. Even numbered columns should be small letters too. I don't know how to avoid using same letters. I tried to send the letters used to another array made of one dimension, then check every letter sent by it so that same letter won't be used but my coding skills didn't let me do it.
So, my code is this so far:
#include <iostream>
#include <iomanip>
#include <stdlib.h>
#include <ctime>
#include <locale.h>
using namespace std;
const int row = 5;
const int column = 10;
int main()
{
char matris[row][column];
srand(time(0));
for (int i = 0; i < row; i++)
for (int j = 0; j < column; j++)
if(j % 2 == 0)
matris[i][j] = rand() % 25 + 65;
else
matris[i][j] = rand() % 25 + 97;
for (int i = 0; i < row; i++)
{
for (int j = 0; j < column; j++)
cout << setw(5) << matris[i][j];
cout << endl;
}
system("pause");
return 0;
}
So, how can I avoid using same letters? Did I approach wrongly? Is there a easier way to do what I'm trying to do? Thanks...
A possible solution is to create a vector containing all the symbols you want to use, randomized it, then draw from that. Example
#include <iostream>
#include <algorithm>
#include <vector>
#include <random>
using namespace std;
struct CharPool
{
size_t pos;
vector<char> m_unused_char;
CharPool()
: pos(0)
{
// add whatever characters you like to the pool
for (char c = 'a'; c <= 'z'; ++c)
m_unused_char.push_back(c);
for (char c = 'A'; c <= 'Z'; ++c)
m_unused_char.push_back(c);
std::random_device rd;
std::mt19937 g(rd());
// randomize
shuffle(m_unused_char.begin(), m_unused_char.end(), g);
}
char next()
{
// here we should assert that the pool is not depleted
return m_unused_char[pos++];
}
};
int main()
{
CharPool pool;
for (size_t i = 0; i < 10; ++i)
cout << pool.next() << ", ";
cout << "\n";
}
You need to keep trace of the chars that already appeared, to do so you can use a std::set , at each random call, you check if the random result is inside the set: if it is you simply random another number and retry; if not, you insert it and put it in your matrix.
I'd use a set rather than a vector because it's faster when checking if a value already appears in it.
See this to know how to check if a set contains an element:
How to check that an element is in a std::set?

linear search for number vector in c++

I am trying to output 9 random non repeating numbers. This is what I've been trying to do:
#include <iostream>
#include <cmath>
#include <vector>
#include <ctime>
using namespace std;
int main() {
srand(time(0));
vector<int> v;
for (int i = 0; i<4; i++) {
v.push_back(rand() % 10);
}
for (int j = 0; j<4; j++) {
for (int m = j+1; m<4; m++) {
while (v[j] == v[m]) {
v[m] = rand() % 10;
}
}
cout << v[j];
}
}
However, i get repeating numbers often. Any help would be appreciated. Thank you.
With a true random number generator, the probability of drawing a particular number is not conditional on any previous numbers drawn. I'm sure you've attained the same number twice when rolling dice, for example.
rand(), which roughly approximates a true generator, will therefore give you back the same number; perhaps even consecutively: your use of % 10 further exacerbates this.
If you don't want repeats, then instantiate a vector containing all the numbers you want potentially, then shuffle them. std::shuffle can help you do that.
See http://en.cppreference.com/w/cpp/algorithm/random_shuffle
When j=0, you'll be checking it with m={1, 2, 3}
But when j=1, you'll be checking it with just m={2, 3}.
You are not checking it with the 0th index again. There, you might be getting repetitions.
Also, note to reduce the chances of getting repeated numbers, why not increase the size of random values, let's say maybe 100.
Please look at the following code to get distinct random values by constantly checking the used values in a std::set:
#include <iostream>
#include <vector>
#include <set>
int main() {
int n = 4;
std::vector <int> values(n);
std::set <int> used_values;
for (int i = 0; i < n; i++) {
int temp = rand() % 10;
while (used_values.find(temp) != used_values.end())
temp = rand() % 10;
values[i] = temp;
}
for(int i = 0; i < n; i++)
std::cout << values[i] << std::endl;
return 0;
}

2D Vectors Char to Int

I am trying to convert a 2D Vectors of randomly generated chars to int. For example, if the chars are 'abc' then I want my int vector to be '97,98,99' etc.
I tried looking on here and for the most part, people are asking about char to sting, string to char, etc.
This is what I have so far.
#include <vector>
#include <cstdlib>
#include <string>
#include <iostream>
using namespace std;
int main()
{
vector<vector<char> > vec(100, vector<char>(10));
vector<vector<int> > intVec(100, vector<int>(10));
srand(time(NULL));
int intAscii = 0;
// Fill 2D vector with random chars
for(int i = 0; i < 1; i++)
{
rand_num = (rand() % 8 + 3);
for(int j = 0; j < rand_num; j++)
{
//logic here... randomly gen a char and place it in the same position, but this time in the int vector as an int.
vec.at(i).push_back((rand() % 26 + 97));
intAscii = int(vec.at(i).at(j));
intVec.at(i).push_back(intAscii);
}
// Print Contents & print out the int vector.
for(int i = 0; i < vec.size(); i++)
{
for(int j = 0; j < vec.at(i).size(); j++)
{
cout << vec.at(i).at(j);
cout << intVec.at(i).at(j);
}
}
}
The problem that I am running into is that when it prints out both vectors, chars is fine, for int I am getting a whole bunch of zeros. Which doesn't seem right because the int(vec.at(i).at(j)) works i.e if char vector was a then the int vector would be 97 and so on.
At this point, my guess is that the syntax for the int vector might be wrong.
You may try this:
intAscii = (int)vec.at(i).at(j);
In addition, to access the elements it could be better to use indices instead of push_back, like:
intVec.at(i).at(j) = intAscii;
This should work because you already allocate memory for your vector at the very beginning.

Vector inside vector (creating chromosomes)

I'm attempting to build a genetic algorithm that can take a certain amount of variables (say 4), and use these in a way so that you could have 2a + 3b + c*c + d = 16. I realise there are more efficient ways to calculate this, but I want to try and build a genetic algorithm to expand later.
I'm starting by trying to create "organisms" that can compete later. What I've done is this:
#include "stdafx.h"
#include <iostream>
#include <vector>
#include <random>
// Set population size
const int population_size = 10;
const int number_of_variables = 4;
int main()
{
// Generate random number
std::random_device rd;
std::mt19937 rng(rd()); // random-number engine (Mersenne-Twister in this case)
std::uniform_int_distribution<int> uni(-10, 10);
// Set gene values.
std::vector<int>chromosome;
std::vector<int>variables;
for (int i = 0; i < number_of_variables; ++i)
{
double rand_num = uni(rng);
variables.push_back (rand_num);
std::cout << variables[i] << "\n";
}
return 0;
}
What happens is it will fill up the number_of_variables vector, and output these just because that makes it clear for me that it's actually doing what I intend for it to do. What I want it to do however is to fill up each "chromosome" with one variables vector, so that for example chromosome 0 would have the values {1, 5, -5, 9} etc.
The following code obviously isn't working, but this is what I'd like it to do:
for (int j = 0; j < population_size; ++j)
{
for (int i = 0; i < number_of_variables; ++i)
{
double rand_num = uni(rng);
variables.push_back(rand_num);
}
chromosome.push_back(variables[j]);
std::cout << chromosome[j] << "\n";
}
Meaning it'd fill up the variables randomly, then chromosome1 would take those 4 values that "variables" took, and repeat. What actually happens is that (I think) it only takes the first value from "variables" and copies that into "chromosome" rather than all 4.
If anyone could help it'd be very much appreciated, I realise this might be simply a rookie mistake that is laughably simply in the eyes of someone more experienced with vectors (which would probably be 99% of the people on this website, hah).
Anyway, thanks :)
#include <iostream>
#include <vector>
#include <random>
// Set population size
const int population_size = 10;
const int number_of_variables = 4;
int main()
{
// Generate random number
std::random_device rd;
std::mt19937 rng(rd()); // random-number engine (Mersenne-Twister in this case)
std::uniform_int_distribution<int> uni(-10, 10);
// Set gene values.
std::vector< std::vector<int>>chromosome;
for( int kp = 0; kp < population_size; kp++ )
{
std::vector<int>variables;
for (int i = 0; i < number_of_variables; ++i)
{
double rand_num = uni(rng);
variables.push_back (rand_num);
}
chromosome.push_back( variables );
}
// display entire population
for( auto c : chromosome )
{
for( auto v : c )
{
std::cout << v << " ";
}
std::cout << "\n";
}
// display 4th member of population
for( auto v : chromosone[ 3 ] )
{
std::cout << v << " ";
}
std::cout << "\n";
return 0;
}
http://ideone.com/2jastJ
You can place a vector inside a vector with the syntax:
std::vector<std::vector<int>>
but you will need to make the outer vector large enough for num_variables.
#include <vector>
#include <cstdlib>
using Individual = std::vector<int>;
using Population = std::vector<Individual>;
// short for std::vector<std::vector<int>>;
const size_t number_of_variables = 8;
int main() {
Population population(10);
for (auto& individual : population) {
individual.resize(number_of_variables);
for (size_t j = 0; j < number_of_variables; ++j) {
individual[j] = j; // replace with random number
}
}
}
Live demo: http://ideone.com/pfufGt