九度oj1109

 http://ac.jobdu.com/problem.php?id=1109

#include <stdio.h>#include <string.h>#include <stdlib.h>#include <math.h>int a[1001][1001];int visited[1001];void dfs(int start,int n){int j;visited[start] = 1;for(j=0;j<n;j++)if(a[start][j] == 1 && visited[j] == 0)dfs(j,n);}int main(){  int x,y,n,m;int i,j,flag;while(scanf("%d %d",&n,&m) != EOF && (n != 0)){flag = 1;for(i=0;i<n;i++)for(j=0;j<n;j++)a[i][j] = 0;for(i=0;i<n;i++)visited[i] = 0;for(i=1;i<=m;i++){scanf("%d %d",&x,&y);a[x-1][y-1] = 1;a[y-1][x-1] = 1;}dfs(x-1,n);for(i=0;i<n;i++){if(visited[i] == 0){flag = 0;break;}}if(flag == 1)printf("YES\n");elseprintf("NO\n");}return 0;}