【HDOJ】2444 The Accomodation of Students

图论的题目。着色原理+二分图匹配。

 1 #include <cstdio>
 2 #include <cstring>
 3
 4 #define MAXN 205
 5
 6 char map[MAXN][MAXN];
 7 int link[MAXN];
 8 int color[MAXN];
 9 bool visit[MAXN];
10 int n, m;
11
12 bool dfs(int v, int col) {
13     int i;
14
15     for (i=1; i<=n; ++i) {
16         if (map[i][v]) {
17             if (color[i] == col)
18                 return false;
19             else if (color[i] == 0) {
20                 color[i] = -col;
21                 if (dfs(i, -col) == false)
22                     return false;
23             }
24         }
25     }
26     return true;
27 }
28
29 bool find(int v) {
30     int i;
31
32     for (i=1; i<=n; ++i) {
33         if (!visit[i] && map[i][v]) {
34             visit[i] = true;
35             if (link[i]==0 || find(link[i])) {
36                 link[i] = v;
37                 return true;
38             }
39         }
40     }
41     return false;
42 }
43
44 int main() {
45     int ans;
46     int i, j;
47
48     while (scanf("%d%d", &n, &m) != EOF) {
49         memset(map, 0, sizeof(map));
50         memset(link, 0, sizeof(link));
51         memset(color, 0, sizeof(color));
52         while (m--) {
53             scanf("%d %d", &i, &j);
54             map[i][j] = map[j][i] = 1;
55         }
56         color[1] = 1;
57         if (dfs(1, 1) == false) {
58             printf("No\n");
59             continue;
60         }
61         for (ans=0, i=1; i<=n; ++i) {
62             memset(visit, false, sizeof(visit));
63             if (find(i))
64                 ++ans;
65         }
66         printf("%d\n", ans/2);
67     }
68
69     return 0;
70 }

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