HDU DFS

Rikka with Graph II

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)

Total Submission(s): 887    Accepted Submission(s): 222


Problem Description

As we know, Rikka is poor at math. Yuta is worrying about this situation, so he gives Rikka some math tasks to practice. There is one of them:

Yuta has a non-direct graph with n vertices
and n edges.
Now he wants you to tell him if there exist a Hamiltonian path.

It is too difficult for Rikka. Can you help her?

 

Input

There are no more than 100 testcases. 

For each testcase, the first line contains a number n(1≤n≤1000).

Then n lines
follow. Each line contains two numbers u,v(1≤u,v≤n) ,
which means there is an edge between u and v.

 

Output

For each testcase, if there exist a Hamiltonian path print "YES" , otherwise print "NO".

 

Sample Input

4
1 1
1 2
2 3
2 4
3
1 2
2 3
3 1

 

Sample Output

NO
YES
注意统计度数 大于2直接错 还有初始化
#include<cstdio>
#include<iostream>
using namespace std;
int map[1005][1005]={0};
int sum=1;
bool used[1005]={0};
int du[1005]={0};
int n=0;
bool mark=0;
void dfs(int x);
int main()
{
while(scanf("%d",&n)!=EOF)
{
mark=0;
sum=1;
memset(used,0,sizeof(used));
memset(du,0,sizeof(du));
memset(map,0,sizeof(map));
for(int i=1;i<=n;i++)
{
int a=0,b=0;
scanf("%d%d",&a,&b);
if(a!=b&&!map[a][b])
{
map[a][b]=map[b][a]=1;
du[a]++;
du[b]++;
}
}
int top=0;
int s=1;
for(int i=1;i<=n;i++)
{
if(du[i]==1)
{
 s=i;
 top++;
   }
}
   if(top>2)
   {
    printf("NO\n");
    continue;
   }
   used[s]=1;
   dfs(s);
   if(mark)
   {
     printf("YES\n");
   }
   else
   {
    printf("NO\n");
   }
  
}
return 0;
}
void dfs(int x)
{
if(sum==n){mark=1;return;}
for(int i=1;i<=n&&!mark;i++)
{
if(!used[i]&&map[x][i])
{
used[i]=1;
sum++;
dfs(i);
sum--;
used[i]=0;
}
}
}