UVA - 11520 Fill the Square ( 貪心 )

#include <iostream>
#include <cstring>
#include <string>
#include <cctype>
#define rep(i, k, n) for (int i = k; i < (n); i++)
#define Clear(x, y) memset(x, y, sizeof(x))
using namespace std;
const int N = 15;
int used[26]; //用於存放 26 個字母中，哪些可用
char map[N][N]; 
int d[4][2] = {0,1,1,0,-1,0,0,-1};
int n, m;
bool isin (int i, int j)
{
	return i >= 0 && i < m && j >= 0 && j < m;
}
int main()
{
	cin >> n;
	rep(t, 0, n)
	{
		cin >> m;
		rep(i, 0, m)
		rep(j, 0, m)
		cin >> map[i][j];
		rep(i, 0, m)
		rep(j, 0, m) //對於每個爲  '.' 的位置，先將它四周用過的字母記錄下來，貪心選擇該位置可用，且爲當前可選字母中最小的字母 
		{
			if ( map[i][j] == '.')
			{
				Clear(used, 0);
				rep(k, 0, 4) //將 . 四周的英文字母做標記 
				{
					int ii = i + d[k][0], jj = j + d[k][1];
					if (isin(ii, jj))
					{
						char ch = map[ii][jj];
						if (isupper(ch))
						used[ch - 'A'] = 1;
					}
				}
				rep(k, 0, 26) //貪心選擇當前可用的最小字符
				{
					if (!used[k])
					{
						map[i][j] = k + 'A';
						break;
					}	
				} 
			}
		}
		cout << "Case " << t + 1 << ":" << endl;
		rep(i, 0, m)
		{
			rep(j, 0, m)
			cout << map[i][j];
			cout << endl;
		}
	}
	return 0;
}