枚举 POJ 1753 Flip Game

题目地址：http://poj.org/problem?id=1753

 /*
     这题几乎和POJ 2965一样，DFS函数都不用修改
     只要修改一下change规则。。。
     注意：是否初始已经ok了要先判断
 */
 #include <cstdio>
 #include <iostream>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 #include <string>
 #include <map>
 #include <queue>
 #include <vector>
 using namespace std;

 const int MAXN = 1e6 + ;
 const int INF = 0x3f3f3f3f;
 int a[][];
 bool flag;

 bool ok(void)
 {
     int tmp = a[][];
     for (int i=; i<=; ++i)
     {
         for (int j=; j<=; ++j)
             if (a[i][j] != tmp)    return false;
     }

     return true;
 }

 void change(int x, int y)
 {
     a[x][y] = !a[x][y];
     if (x > )    a[x-][y] = !a[x-][y];
     if (x < )    a[x+][y] = !a[x+][y];
     if (y > )    a[x][y-] = !a[x][y-];
     if (y < )    a[x][y+] = !a[x][y+];
 }

 void DFS(int x, int y, int num, int cnt)
 {
     if (num == cnt)
     {
         flag = ok ();
         return ;
     }
     for (int i=x; i<=; ++i)
     {
         int j;
         if (i == x)    j = y + ;
         else    j = ;
         for (; j<=; ++j)
         {
             change (i, j);
             DFS (i, j, num+, cnt);
             if (flag)    return ;
             change (i, j);
         }
     }
 }

 void work(void)
 {
     if (ok ())
     {
         printf ("%d\n", );        return ;
     }
     int cnt;
     for (cnt=; cnt<=; ++cnt)        //最多16次，可以暴力枚举
     {
         flag = false;
         DFS (, , , cnt);
         if (flag)    break;
     }
     (cnt <= ) ? printf ("%d\n", cnt) : puts ("Impossible");
 }

 int main(void)        //POJ 1753 Flip Game
 {
     //freopen ("A.in", "r", stdin);

     char ch;
     for (int i=; i<=; ++i)
     {
         for (int j=; j<=; ++j)        //b-0 w-1
         {
             scanf ("%c", &ch);
             a[i][j] = (ch == 'b') ?  : ;
         }
         getchar ();
     }

     work ();

     return ;
 }

 /*
 Impossible
 */