ACM学习历程—HDU5423 Rikka with Tree（搜索）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <set>
#include <queue>
#include <vector>
#define LL long long

using namespace std;

const int maxN = 1005;

struct Edge
{
    int to, next;
    //int val;
}edge[maxN*2];

int head[maxN], cnt;

void addEdge(int u, int v)
{
    edge[cnt].to = v;
    edge[cnt].next = head[u];
    head[u] = cnt;
    cnt++;
}

void initEdge()
{
    memset(head, -1, sizeof(head));
    cnt = 0;
}

int n;
bool vis[maxN];
int maxDepth;
bool flag;

bool input()
{
    if (scanf("%d", &n) == EOF)
        return false;
    initEdge();
    memset(vis, false, sizeof(vis));
    maxDepth = 0;
    flag = true;
    int u, v;
    for (int i = 1; i < n; ++i)
    {
        scanf("%d%d", &u, &v);
        addEdge(u, v);
        addEdge(v, u);
    }
    return true;
}

void dfs(int now, int depth)
{
    if (flag == false)
        return;
    int cnt = 0;
    vis[now] = true;
    for (int i = head[now]; i != -1; i = edge[i].next)
    {
        if (vis[edge[i].to])
            continue;
        dfs(edge[i].to, depth+1);
        cnt++;
    }
    if (cnt == 0)
        return;
    maxDepth = max(maxDepth, depth);
    if (depth != maxDepth && cnt != 1)
        flag = false;
}

void work()
{
    dfs(1, 0);
    if (flag)
        printf("YES\n");
    else
        printf("NO\n");
}

int main()
{
    //freopen("test.in", "r", stdin);
    while (input())
    {
        work();
    }
    return 0;
}