11520 - Fill the Square, uva, solution

#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
#include<set>
#include<algorithm>
#define db(a) cout << #a << " = " << a << endl
#define db2(a, b) cout << #a << " = " << a << " " << #b << " = " << b << endl
#define listar(lista) for (int i = 0; i < lista.size(); i++) db(lista[i])
#define foreach(it, l) for (typeof(l.begin()) it = l.begin(); it != l.end(); it++)
using namespace std;
int dirx[] = {0, 0, -1, 1};
int diry[] = {-1, 1, 0, 0};
vector<string> matriz;
int n;
void llenar (int x, int y) {
 if (x < 0 || x >= n || y < 0 || y >= n || matriz[x][y] != '.') return;
 for (char i = 'A'; i < 'Z' + 1; i++) {
  bool can = true;
  for (int k = 0; k < 4; k++) {
   if (x + dirx[k] >= 0 && 
    x + dirx[k] < n &&
    y + diry[k] >= 0 &&
    y + diry[k] < n && matriz[x + dirx[k]][y + diry[k]] == i)
    can = false;
  }
  if (can)  {
   matriz[x][y] = i;
   break;
  }
 } 
}
int main() {
 int t, caso;
 #ifdef dennisbot
  freopen("in.in", "r", stdin);
  freopen("ou.out", "w", stdout);
 #endif
 scanf("%d", &t);
 caso = t;
 while (t--) {
  scanf("%d", &n);
  matriz.resize(n);
  for (int i = 0; i < n; i++) {
   cin >> matriz[i];
  }
  for (int i = 0; i < n; i++) {
   for (int j = 0; j < n; j++) {
    llenar(i, j);
   }
  }
  
  printf("Case %d:\n", caso - t);
  
  for (int i = 0; i < n; i++) {
   cout << matriz[i] << endl;
  }
  
 }
 return 0;
}