C++ Programming Code Examples
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Generate All Possible Combinations of a Given List of Numbers
/* Generate All Possible Combinations of a Given List of Numbers
- This algorithm print all the possible combination of each length from the given array.
- The time complexity of this algorithm is O(n*(2^n)).
- This algorithm takes the input of 'n' data element and prints all possible combination.
- For that, it maintains a boolean array of length 'n'.
- If the corresponding boolean value is true, then it prints that element.
- Exit. */
#include<iostream>
using namespace std;
// A function to print all combination of a given length from the given array.
void Combination(int a[], int reqLen, int start, int currLen, bool check[], int len)
{
// Return if the currLen is more than the required length.
if(currLen > reqLen)
return;
// If currLen is equal to required length then print the sequence.
else if (currLen == reqLen)
{
cout<<"\t";
for (int i = 0; i < len; i++)
{
if (check[i] == true)
{
cout<<a[i]<<" ";
}
}
cout<<"\n";
return;
}
// If start equals to len then return since no further element left.
if (start == len)
{
return;
}
// For every index we have two options.
// First is, we select it, means put true in check[] and increment currLen and start.
check[start] = true;
Combination(a, reqLen, start + 1, currLen + 1, check, len);
// Second is, we don't select it, means put false in check[] and only start incremented.
check[start] = false;
Combination(a, reqLen, start + 1, currLen, check, len);
}
int main()
{
int i, n;
bool check[n];
cout<<"Enter the number of element array have: ";
cin>>n;
int arr[n];
cout<<"\n";
// Take the input of the array.
for(i = 0; i < n; i++)
{
cout<<"Enter "<<i+1<<" element: ";
cin>>arr[i];
check[i] = false;
}
// For each length of sub-array, call the Combination().
for(i = 1; i <= n; i++)
{
cout<<"\nThe combination of length "<<i<<" for the given array set:\n";
Combination(arr, i, 0, 0, check, n);
}
return 0;
}
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