HDU 4751 Divide Groups

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cmath>
 5 #include <algorithm>
 6 #include <climits>
 7 #include <vector>
 8 #include <queue>
 9 #include <cstdlib>
10 #include <string>
11 #include <set>
12 #include <stack>
13 #define LL long long
14 #define pii pair<int,int>
15 #define INF 0x3f3f3f3f
16 using namespace std;
17 const int maxn = 110;
18 int g[maxn][maxn],color[maxn],n;
19 bool bfs(int v) {
20     queue<int>q;
21     color[v] = 0;
22     q.push(v);
23     while(!q.empty()) {
24         int u = q.front();
25         q.pop();
26         for(int i = 1; i <= n; ++i) {
27             if(i == u || g[u][i] == 2) continue;
28             if(color[i] == -1) {
29                 color[i] = color[u]^1;
30                 q.push(i);
31             } else if(color[i] == color[u]) return false;
32         }
33     }
34     return true;
35 }
36 int main() {
37     while(~scanf("%d",&n)) {
38         memset(g,0,sizeof(g));
39         memset(color,-1,sizeof(color));
40         for(int i = 1; i <= n; ++i) {
41             int j = 0;
42             while(scanf("%d",&j),j) {
43                 g[i][j]++;
44                 g[j][i]++;
45             }
46         }
47         bool flag = true;
48         for(int i = 1; i <= n; ++i)
49             if(color[i] == -1) {
50                 flag = bfs(i);
51                 if(!flag) break;
52             }
53         if(flag) puts("YES");
54         else puts("NO");
55     }
56     return 0;
57 }