hdu4715

题解：

二分图判断

建立原图的补图

判断是否是二分图

代码：

#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=;
int an[N],ans,a[N][N],n,x;
void dfs(int x,int y)
{
    if (ans)return;
    an[x]=y;
    for (int i=;i<=n;i++)
     if ((!a[x][i]||!a[i][x])&&i!=x)
      {
          if (an[i]&&-y!=an[i]){ans=;return;}
          if (!an[i])dfs(i,-y);
      }
}
int main()
{
    while (~scanf("%d",&n))
     {
         ans=;
         memset(an,,sizeof an);
         memset(a,,sizeof a);
         for (int i=;i<=n;i++)
          for (scanf("%d",&x);x;scanf("%d",&x))a[i][x]=;
         for (int i=;i<=n;i++)
         if (!an[i])dfs(i,);
        if (ans)puts("NO");else puts("YES");
     }
}