[POJ2446] Chessboard（二分图最大匹配-匈牙利算法）

 1 #include <cstdio>
 2 #include <cstring>
 3 
 4 using namespace std;
 5 
 6 const int MAXN = 1001;
 7 int n, m, cnt, t, tot, k1, k2;
 8 int head[10001], to[10001], next[10001], belong[10001], map[MAXN][MAXN];
 9 int dx[4] = {0, 1, -1, 0},
10     dy[4] = {1, 0, 0, -1};
11 bool b[MAXN][MAXN], vis[10001];
12 
13 inline void add(int x, int y)
14 {
15     to[cnt] = y;
16     next[cnt] = head[x];
17     head[x] = cnt++;
18 }
19 
20 inline int find(int u)
21 {
22     int i, v;
23     for(i = head[u]; i != -1; i = next[i])
24     {
25         v = to[i];
26         if(!vis[v])
27         {
28             vis[v] = 1;
29             if(!belong[v] || find(belong[v]))
30             {
31                 belong[v] = u;
32                 return 1;
33             }
34         }
35     }
36     return 0;
37 }
38 
39 int main()
40 {
41     int i, j, k, x, y;
42     while(~scanf("%d %d %d", &n, &m, &t))
43     {
44         k1 = k2 = 0;
45         memset(head, -1, sizeof(head));
46         memset(belong, 0, sizeof(belong));
47         memset(b, 0, sizeof(b));
48         for(i = 1; i <= t; i++)
49         {
50             scanf("%d %d", &x, &y);
51             b[y - 1][x - 1] = 1;
52         }
53         for(i = 0; i < n; i++)
54             for(j = 0; j <= m; j++)
55             if(!b[i][j])
56                 if((i + j) % 2 == 1) map[i][j] = ++k1;
57                 else map[i][j] = ++k2;
58         for(i = 0; i < n; i++)
59             for(j = 0; j < m; j++)
60                 if(!b[i][j] && (i + j) % 2 == 1)
61                 for(k = 0; k <= 3; k++)
62                 {
63                     x = i + dx[k];
64                     y = j + dy[k];
65                     if(x >= 0 && x < n && y >= 0 && y < m && !b[x][y])
66                         add(map[i][j], map[x][y]);
67                 }
68         for(i = 1; i <= k1; i++)
69         {
70             memset(vis, 0, sizeof(vis));
71             if(find(i)) tot++;
72         }
73         if(2 * tot + t == n * m) printf("YES\n");
74         else printf("NO\n");
75     }
76     return 0;
77 }