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uva 10503

這題讓我太驚訝了，打個DFS隨便提交竟然AC

不過我對這題感覺模糊模糊的，感覺上像是靠測資知道意思的

[sourcecode language="cpp"][/sourcecode]


//============================================================================
// Name : The dominoes solitaire.cpp
// Date : 2013 2013/2/6 下午4:32:17
// Author : GCA
//============================================================================
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <climits>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cctype>
#include <utility>
using namespace std;
typedef long long ll;
typedef unsigned int uint;
#define Set(a,s) memset(a,s,sizeof(a))
#define Write(w) freopen(w,"w",stdout)
#define Read(r) freopen(r,"r",stdin)
#define Pln() printf("\n")
#define I_de(x,n)for(int i=0;i<n;i++)printf("%d ",x[i]);Pln()
#define De(x)printf(#x"%d\n",x)
#define For(i,x)for(int i=0;i<x;i++)
#define CON(x,y) x##y
#define Pmz(dp,nx,ny)for(int hty=0;hty<ny;hty++){for(int htx=0;htx<nx;htx++){\
printf("%d ",dp[htx][hty]);}Pln();}
#define M 15
#define PII pair<int,int>
#define PB push_back
#define oo INT_MAX
#define Set_oo 0x3f
#define Is_debug true
#define debug(...) if(Is_debug)printf("DEBUG: "),printf(__VA_ARGS__)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define eps 1e-6
bool xdy(double x,double y){return x>y+eps;}
bool xddy(double x,double y){return x>y-eps;}
bool xcy(double x,double y){return x<y-eps;}
bool xcdy(double x,double y){return x<y+eps;}
int min3(int x,int y,int z){
int tmp=min(x,y);
return min(tmp,z);
}
int max3(int x,int y,int z){
int tmp=max(x,y);
return max(tmp,z);
}
int n,m;
int path[M][2];
int st[2],ed[2];
bool vis[M];//edge traversal
int k;
int judge=0;
void dfs(int now,int depth){
// debug(">>>now%d depth%d j%d\n",now,depth,judge);
if(judge)return;
if(depth==n&&now==ed[0]){
judge=1;
return;
}
else if(depth>=n)return;
for(int i=0;i<k;i++){
if(now==path[i][0]&&!vis[i]){
vis[i]=1;
dfs(path[i][1],depth+1);
vis[i]=0;
}
else if(now==path[i][1]&&!vis[i]){
vis[i]=1;
dfs(path[i][0],depth+1);
vis[i]=0;
}
}
}
int main() {
ios_base::sync_with_stdio(0);
while(~scanf("%d",&n)&&n){
scanf("%d",&m);
k=0,judge=0;
Set(vis,0);
scanf("%d%d",&st[0],&st[1]);
scanf("%d%d",&ed[0],&ed[1]);
while(m--){
int x,y;
scanf("%d%d",&x,&y);
path[k][0]=x,path[k++][1]=y;
}
dfs(st[1],0);
if(judge)printf("YES\n");
else printf("NO\n");
// debug("