hdu 5424 Rikka with Graph II 判n点n边的图是否为哈密顿通路

题意：给n个点n条边，判断图是否为哈密顿通路。

直接暴力搜

//author: CHC
//First Edit Time: 2015-08-30 16:12
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <set>
#include <vector>
#include <map>
#include <queue>
#include <set>
#include <algorithm>
#include <limits>
using namespace std;
typedef long long LL;
const int MAXN=1010;
const int INF = numeric_limits<int>::max();
const LL LL_INF= numeric_limits<LL>::max();
struct Edge {
    int to,next;
    Edge(){}
    Edge(int _to,int _next):to(_to),next(_next){}
}e[MAXN*2];
int head[MAXN],tot;
void init(){
    memset(head,-1,sizeof(head));
    tot=0;
}
void AddEdge(int u,int v){
    e[tot]=Edge(v,head[u]);
    head[u]=tot++;
    e[tot]=Edge(u,head[v]);
    head[v]=tot++;
}
int vis[MAXN],n;
void dfs1(int u){
    vis[u]=1;
    for(int i=head[u];~i;i=e[i].next){
        if(!vis[e[i].to])dfs1(e[i].to);
    }
}
bool dfs2(int u,int d){
    if(d==n) return true;
    for(int i=head[u];~i;i=e[i].next){
        int v=e[i].to;
        if(!vis[v]){
            vis[v]=1;
            if(dfs2(v,d+1))return true;
            vis[v]=0;
        }
    }
    return false;
}
int mapp[MAXN][MAXN],du[MAXN];
int main()
{
    while(~scanf("%d",&n)){
        memset(mapp,0,sizeof(mapp));
        for(int i=1;i<=n;i++) mapp[i][i]=1;
        memset(du,0,sizeof(du));
        init();
        for(int i=1,x,y;i<=n;i++){
            scanf("%d%d",&x,&y);
            if(!mapp[x][y]){
                mapp[x][y]=mapp[y][x]=1;
                AddEdge(x,y);
                ++du[x];++du[y];
            }
        }
        memset(vis,0,sizeof(vis));
        dfs1(1);
        int s=1,flag=0,cnt1=0,cnt3=0;
        for(int i=1;i<=n;i++){
            if(!vis[i])flag=1;
            if(du[s]>du[i])s=i;
            if(du[i]==1)++cnt1;
            else if(du[i]==3)++cnt3;
            else if(du[i]==0&&n!=1)flag=1;
            if(cnt1>2)flag=1;
            if(cnt3>2)flag=1;
        }
        //printf("s:%d\n",s);
        memset(vis,0,sizeof(vis));
        vis[s]=1;
        if(flag)puts("NO");
        else if(dfs2(s,1))puts("YES");
        else puts("NO");
    }
    return 0;
}