grid sorting greedy approach

grid_sorting.cpp

string gridChallenge(vector<string> grid) {
  size_t jj, n = grid.size();
    bool is_not = false;
    for (int i = n-1; i >= 0; i--) {
        string& r = grid[i];
 
        sort(begin(r),end(r));
 
        if (i == n-1) continue;
        string& p = grid[i+1];
 
         for (int j = 0; j < n; j++) {
 
             if (int(r[j]) > int(p[j])) {
                 is_not = true; break;
             }
         }
        if (is_not) break;
    }
    return (is_not?"NO":"YES");
}