【模板】判断二分图

 1 #include <cstdio>
 2 #include <cstring>
 3 
 4 int n, e, cnt;
 5 int head[1001], next[1001], to[1001], color[1001];
 6 
 7 void add(int x, int y)
 8 {
 9     to[cnt] = y;
10     next[cnt] = head[x];
11     head[x] = cnt++;
12 }
13 
14 bool dfs(int u, int c)
15 {
16     int i, v;
17     color[u] = c;
18     for(i = head[u]; i != -1; i = next[i])
19     {
20         v = to[i];
21         if(color[v] == c) return 0;
22         if(color[v] == 0 && !dfs(v, -c)) return 0;
23     }
24     return 1;
25 }
26 
27 bool solve()
28 {
29     int i;
30     for(i = 1; i <= n; i++)
31      if(color[i] == 0 && !dfs(i, 1))
32       return 0;
33     return 1;
34 }
35 
36 int main()
37 {
38     int i, x, y;
39     scanf("%d %d", &n, &e);
40     memset(head, -1, sizeof(head));
41     for(i = 1; i <= e; i++)
42     {
43         scanf("%d %d", &x, &y);
44         add(x, y);
45         add(y, x);
46     }
47     if(solve()) printf("YES");
48     else printf("NO");
49     return 0;
50 }