hdu 5423 Rikka with Tree

參考：http://blog.csdn.net/aaaaacmer/article/details/48093767

#include <stdio.h>
#include <string.h>
#include <algorithm>
#define M 1005

using namespace std;

struct node{
    int to, next;
}edge[M*100];

int head[M*2];
int n, tot, ans[1005], q, vis[1005];

void add(int a, int b){
    edge[tot].to = b;
    edge[tot].next = head[a];
    head[a] = tot++;
}

int t=0;

void dfs(int x, int deep){
    int i, j;
    vis[x] = 1;
    for(i = head[x]; i != -1; i = edge[i].next){
        j = edge[i].to;
        if(vis[j]) continue;
        vis[j]=1;
        dfs(j, deep+1);
    }
    ans[q++] = deep;
    return ;
}

int main(){
    int i, u, v;
    while(scanf("%d", &n) != EOF){
        q=0;
        memset(vis, 0, sizeof(vis));
        memset(head, -1, sizeof(head));
        tot = 0;
        for( i = 1; i < n; i++){
            scanf("%d%d", &u, &v);
            add(u, v);
            add(v, u);
        }

        int f=0;
        dfs(1, 0);
        int as = 0, mark = 0;
        sort(ans, ans+q-1);
        for(i =1; i<q-1;i++){
            if(ans[i] == ans[i-1]){mark=1; as=ans[i];}
            if(ans[i] > as&&mark) f=1;
        }
        if(f) printf("NO\n");
        else printf("YES\n");
    }
    return 0;
}