第五篇 poj1753 Flip Game

 1 #include<stdio.h>
 2 #include<iostream>
 3 
 4 using namespace std;
 5 
 6 int chess[4][4];
 7 int moves = 17; // 4*4+1
 8 
 9 void buildBoard() {
10     char c;
11     for (int i = 0; i < 4; i++) {
12         for (int j = 0; j < 4; j++) {
13             cin >> c;
14             if (c == ‘w‘) chess[i][j] = 0;
15             else chess[i][j] = 1;
16         }
17     }
18 }
19 
20 void turn(int x, int y) {
21     if (x >= 0 && y >= 0 && x < 4 && y < 4) {
22         chess[x][y] = !chess[x][y];
23     }
24 }
25 
26 void flip(int num) {
27     int i = num / 4;
28     int j = num % 4;
29 
30     turn(i, j);
31     turn(i+1, j);
32     turn(i, j+1);
33     turn(i-1, j);
34     turn(i, j-1);
35 }
36 
37 bool allSame() {
38     int sum = 0;
39     for (int i = 0; i < 4; i++) {
40         for (int j = 0; j < 4; j++) {
41             sum += chess[i][j];
42         }
43     }
44     return !(sum % 16);
45 }
46 
47 void dfs(int pos, int num_flipped) {
48 
49     if (allSame()) {
50         if (num_flipped < moves) moves = num_flipped;
51         return;
52     }
53     if (pos >= 16) return;
54     dfs(pos+1, num_flipped);
55     flip(pos);
56     dfs(pos+1, num_flipped+1);
57     flip(pos);
58 }
59 
60 int main() {
61     buildBoard();
62     dfs(0, 0);
63     if (moves == 17) {
64         cout << "Impossible" << endl;
65     } else {
66         cout << moves << endl;
67     }
68     return 0;
69 }