HDU5424——DFS——Rikka with Graph II

/*
对于一个连通图，有N个顶点，如果有N条边，那么肯定有环
因为N个点如果不成环最多N-1条边。。。然后找最小度的点DFS就行。。。
*/
/************************************************
* Author        :Powatr
* Created Time  :2015-8-31 17:29:13
* File Name     :HDU5424.cpp
************************************************/

#include <cstdio>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <cstring>
#include <cmath>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <bitset>
#include <cstdlib>
#include <ctime>
using namespace std;

#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1 | 1
typedef long long ll;
const int MAXN = 1e3 + 10;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;

int deg[MAXN];
int n;
int mp[MAXN][MAXN];
int vis[MAXN];
vector<int> G[MAXN];
int flag;
void dfs(int u, int num)
{
if(flag == 1) return;
if(num == n){
flag = 1;
return ;
}
for(int i = 0; i < G[u].size(); i++){
int v = G[u][i];
if(!vis[v]){
vis[v] = 1;
dfs(v, num+1);
vis[v] = 0;
}
}
}
int main(){
int u, v;
while(~scanf("%d", &n)){
memset(mp, 0, sizeof(mp));
memset(vis, 0, sizeof(vis));
memset(deg, 0, sizeof(deg));
for(int i = 1; i <= n; i++)
G[i].clear();
for(int i = 1; i <= n; i++){
scanf("%d%d", &u, &v);
if(mp[u][v] == 0 ){
mp[u][v] = mp[v][u] = 1;
G[u].push_back(v);
G[v].push_back(u);
deg[u]++;
deg[v]++;
}
}
int tot = 0;
int id = 1;
for(int i = 1; i <= n; i++)
if(deg[i] == 1){
id = i;
tot++;
}
if(tot > 2){
puts("NO");
continue;
}
flag = 0;
vis[id] = 1;
dfs(id, 1);
printf("%s\n", !flag ? "NO" : "YES");
}
return 0;
}