permutationSequence.cpp

public:
    int fac(int n){  // Compute 'n!'
        int f = 1;
        for(int i = 2; i <= n; i++) f *= i;
        return f;
    }

    string getPermutation(int n, int k) {

        vector<int> v;                              // A dynamic array, to store all numbers
        for(int i = 1; i <= n; i++) v.push_back(i); // from 1 to n "in order".

        string s = "";  // To store final result.

        k--;    // As permutations here start from 0 to (n! - 1)

        while(n--){     // Loop, till all numbers from 1 to n are added in 's'

            int f = fac(n);  // If current position is i, get (n-i)!

            s += to_string(v[k / f]);   // Converting the number we got from 'v' to string and 
                                        // concatenate it to s.

            v.erase(v.begin() + k / f); // Erase the element we got from v to avoid repetition

            k %= f; // 'k' now equals remainder after dividing k by fac(n-i).
        }

        return s; // Return the resultant string.
    }