2.17 自我记录 树的判定

#include<stdio.h>#include<string.h>int sum[30];int num[30][30]={0};int ok=0;void dfs(int x,int y){int i;sum[x]=1;for(i=1;i<=20;i++){if(i==y)continue;if(num[x][i]==1){if(sum[i]==1){ok=1;continue;}dfs(i,x);}}}int main(){int a, b;while(1){ok = 0;memset(sum, 0, sizeof(sum));memset(num, 0, sizeof(num));while(scanf("%d%d",&a,&b)&&(a||b)){num[a][b]=1;num[b][a]=1;}dfs(2,0);if(ok==0){printf("is a tree.\n");}else{printf("is not a tree.\n");}}return 0;}

用深搜做的代码，遇见树结构是心有余悸啊，可惜，这题目是用并查集