Recurrsion.cpp

#include <bits/stdc++.h>
using namespace std;
     
 
// The main recursive method
// to print all possible 
// strings of length k
void printAllKLengthRec(char set[], string prefix,
                                    int n, int k)
{
     
    // Base case: k is 0,
    // print prefix
    if (k == 0)
    {
        cout << (prefix) << endl;
        return;
    }
 
    for (int i = 0; i < n; i++)
    {
        string newPrefix;
         
        // Next character of input added
        newPrefix = prefix + set[i];
         
        // k is decreased, because 
        // we have added a new character
        printAllKLengthRec(set, newPrefix, n, k - 1);
    }
 
}
 
void printAllKLength(char set[], int k,int n)
{
    printAllKLengthRec(set, "", n, k);
}
 
// Driver Code
int main()
{
     
    cout << "First Test" << endl;
    char set1[] = {'a', 'b'};
    int k = 3;
    printAllKLength(set1, k, 2);
     
    cout << "Second Test\n";
    char set2[] = {'a', 'b', 'c', 'd'};
    k = 1;
    printAllKLength(set2, k, 4);
}