 # C++ Programming Code Examples

## C++ > Sorting Searching Code Examples

### 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; } ``` 