HDU 5432 Rikka with Tree (BestCoder Round #53 (div.2))

#include<stdio.h>
#include<string.h>
#include<algorithm>
#define N 1010

using namespace std;

struct Edge
{
    int u, v, cnt, next;
}edge[N * N];

int head[N], j, cnt;
int a[N];//记录各个点的深度
bool vis[N];

void Add(int u, int v)//邻接表
{
    edge[cnt].u = u;
    edge[cnt].v = v;
    edge[cnt].next = head[u];
    head[u] = cnt++;
}

void Init()
{
    memset(head, -1, sizeof(head));
    memset(a, 0, sizeof(a));
    memset(vis, false, sizeof(vis));
    cnt = j = 0;
}

void DFS(int u, int deep)
{
    int v, i;
    vis[u] = true;
    for(i = head[u]; i != -1 ; i = edge[i].next)
    {
        v = edge[i].v;
        if(!vis[v])
        {
            vis[v] = true;
            DFS(v, deep + 1);
        }
    }
    a[j++] = deep;
    return ;
}//查找记录各个点的深度

int cmp(const void *a, const void *b)
{
    return *(int *)a - *(int *)b;
}

int main()
{
    int n, u, v;
    while(~scanf("%d", &n))
    {
        Init();
        for(int i = 1 ; i < n ; i++)
        {
            scanf("%d%d", &u, &v);
            Add(u, v);
            Add(v, u);
        }
        DFS(1, 0);
        qsort(a, j, sizeof(a[0]), cmp);
        int deep = 0, f = 0, fl = 0;
        for(int i = 1 ; i < j ; i++)
        {
            if(a[i - 1] == a[i])
            {
                fl = 1;//如果两个点的深度相同，就存在分支，即标记有分支
                deep = a[i];
            }
            if(fl == 1 && a[i] > deep)
                f = 1;//如果存在分支且分支的下面还有节点则输出NO
        }
        if(f == 0)
            printf("YES\n");
        else
            printf("NO\n");
    }
    return 0;
}