Задача V. Разноцветные диагонали

#include <iostream>
#include <set>
#include <vector>
#include <algorithm>
#include <limits>
#include <string>
#include <queue>

#define ll unsigned long long

using namespace std;

int main() {
    int n;
    cin >> n;
    vector<vector<bool>> free(n , vector<bool>(n , true));
    vector<vector<int>> color(n , vector<int>(n , 0));

    queue<pair<int, int>> q;

    for (int i = 0; i < n; i++) {
        q.push(make_pair(i, i));
        q.push(make_pair(n - i - 1, i));
        free[i][i] = false;
        free[n - i - 1][i] = false;
        free[i][i] = 0;
        free[n - i - 1][i] = 0;
    }

    while (!q.empty()) {
        int x = q.front().first, y = q.front().second;

        if (x + 1 < n && free[x + 1][y] ) {
            color[x + 1][y] = color[x][y] % 25 + 1;
            free[x + 1][y] = false;
            q.push(make_pair(x + 1, y));
        }
        if (x - 1 >= 0 && free[x - 1][y]) {
            color[x - 1][y] = color[x][y] % 25 + 1;
            free[x - 1][y] = false;
            q.push(make_pair(x - 1, y));
        }
        if (y + 1 < n && free[x][y + 1]) {
            color[x][y + 1] = color[x][y] % 25 + 1;
            free[x][y + 1] = false;
            q.push(make_pair(x,y + 1));
        }
        if (y - 1 >= 0 && free[x][y - 1]) {
            color[x][y - 1] = color[x][y] % 25 + 1;
            free[x][y - 1] = false;
            q.push(make_pair(x, y - 1));
        }

        q.pop();
    }

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cout << (char) ('a' + color[i][j]);
        }
        cout << endl;
    }

    return 0;
}