UVA 11396 Claw Decomposition 二分图判定

//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<sstream>
#include<cmath>
#include<climits>
#include<string>
#include<map>
#include<queue>
#include<vector>
#include<stack>
#include<set>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
#define pb(a) push(a)
#define INF 0x1f1f1f1f
#define lson idx<<1,l,mid
#define rson idx<<1|1,mid+1,r
#define PI  3.1415926535898
template<class T> T min(const T& a,const T& b,const T& c) {
    return min(min(a,b),min(a,c));
}
template<class T> T max(const T& a,const T& b,const T& c) {
    return max(max(a,b),max(a,c));
}
void debug() {
#ifdef ONLINE_JUDGE
#else

    freopen("d:\\in1.txt","r",stdin);
    freopen("d:\\out1.txt","w",stdout);
#endif
}
int getch() {
    int ch;
    while((ch=getchar())!=EOF) {
        if(ch!=' '&&ch!='\n')return ch;
    }
    return EOF;
}

const int maxn=333;
int n,m;
vector<int> g[maxn];
int col[maxn];
bool dfs(int u,int color)
{
    col[u]=color;
    for(int i=0;i<3;i++)
    {
        int v=g[u][i];
        if(!col[v])
            dfs(v,3-color);
        else if(col[v]==col[u])return false;
    }
    return true;
}
int main()
{
    while(scanf("%d",&n)!=EOF&&n)
    {
        m=0;
for(int i=0;i<=n;i++)g[i].clear();
        while(1)
        {
            int u,v;
            scanf("%d%d",&u,&v);
            if(u==0&&v==0)break;
            m++;
            g[u].push_back(v);
            g[v].push_back(u);
        }

        int flag=1;
        memset(col,0,sizeof(col));
        for(int i=1;i<=n;i++)
        {
            if(!col[i])
                flag&=dfs(i,1);
        }
        printf("%s\n",flag?"YES":"NO");
    }
    return 0;
}