770A - New Password - CodeForces Solution

#include <iostream>

using namespace std; 
int main() {
	int n, k;
	cin >> n >> k;
	char A[26] = { 'a', 'b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z' };
	string s = "";
	
	for (int i = 0; i < k; i++) {
		s = s + A[i];
	}
	int z = n - k;
	int x = k - 1;
	int a = rand()%k;
	a--;
	while (z > 0) {
		
		while (s[x] == A[a]) {
			if (a >= k-1)//
				a--;//
			else//
				a++;//
		}
		x++;
	
		s = s + A[a];
		z--;
	}

	cout << s << endl;
}