题解 | Is It A Tree?

应该是目前最少的代码了。（喜欢偷懒嘿嘿嘿）

#include <stdio.h>

int main() {
    int a, b;int Case=0;
    while(1) {
        Case++; int rudu[10001]={0};int point[10001]={0};int num=0;int root=0;
        while (scanf("%d %d", &a, &b) != EOF) {
            if (a == 0 && b == 0) break;
            if (a == -1 && b == -1)return 0;
            rudu[b]++;num++;point[a]++;point[b]++;
        }
        if(num==0){
            printf("Case %d is a tree.\n",Case);
            continue;
        }
        for(int i=1;i<=10000;i++){
            if(point[i]!=0&&rudu[i]==0)root++;
            else if(point[i]!=0&&rudu[i]>1){
                printf("Case %d is not a tree.\n",Case);
                root=100;
                break;
            }
        }
        if(root==1)printf("Case %d is a tree.\n",Case);
        else if(root==100) continue;
        else printf("Case %d is not a tree.\n",Case); 
    }
    return 0;
}