The Accomodation of Students

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <algorithm>
 4 #include <cstring>
 5 
 6 using namespace std;
 7 
 8 /* run this program using the console pauser or add your own getch, system("pause") or input loop */
 9 //int main(int argc, char** argv) 
10 
11 #define N 1005
12 
13 int n, m, flag, ans, x, y;
14 int maps[N][N], vis[N], used[N], c[N];
15 
16 int found(int u)
17 {
18     for(int i = 1; i <= n; i++)
19     {
20         if(! vis[i] && maps[u][i])
21         {
22             vis[i] = 1;
23             if(!used[i] || found(used[i]))
24             {
25                 used[i] = u;
26                 return true;
27             }
28         }
29     }
30     return false;
31 }
32 
33 void dfs(int u, int k)  //所谓染色
34 {
35     c[u] = k;
36     for(int i = 1; i <= n; i++)
37     {
38         if(maps[u][i] && !c[i])

41         dfs(i, -k);
42     }
43 }
44 
45 
46 int main()
47 {
48     while(scanf("%d%d", &n, &m) != EOF)
49     {
50         memset(used, 0, sizeof(used));
51         memset(maps, 0, sizeof(maps));
52         memset(c, 0, sizeof(c));
53         
54         ans = flag = 0;
55         
56         while(m--)
57         {
58             scanf("%d%d", &x, &y);
59             maps[x][y] = 1;
60             vis[x] = vis[y] = true;
61         }
62         
63         for(int i = 1; i <= n; i++)
64         {
65             if(!vis[i])
66             continue;
67             else if(!c[i])
68             dfs(i, 1);
69         }
70         for(int i = 1; i <= n; i++)
71         {
72             for(int j = 1; j <= n; j++)
73             {
74                 if(maps[i][j] && c[i]+c[j])   //一个集合里有认识的人了，flag = 1
75                     flag = 1;
76             }
77         }
78         if(flag)
79         printf("No\n");
80         else
81         {
82             for(int i = 1; i <= n; i++)
83             {
84                 memset(vis, 0, sizeof(vis));
85                 if(found(i) && c[i])
86                 ans++;
87             }
88             printf("%d\n", ans);
89         }
90     }
91     return 0;
92 }