Problem Description

Bobo has a tree,whose vertices are conveniently labeled by 1,2,...,n.Each node has a weight wi.
All the weights are distrinct.
A set with m nodes v1,v2,...,vm is
a Bobo Set if:
- The subgraph of his tree induced by this set is connected.
- After we sort these nodes in set by their weights in ascending order,we get u1,u2,...,um,(that
is,wui<wui+1 for
i from 1 to m-1).For any node x in
the path from ui to ui+1(excluding ui and ui+1),should
satisfy wx<wui.
Your task is to find the maximum size of Bobo Set in a given tree.

 

Input

The input consists of several tests. For each tests:
The first line contains a integer n (1≤n≤500000).
Then following a line contains n integers w1,w2,...,wn (1≤wi≤109,all
the wi is
distrinct).Each of the following n-1 lines contain 2 integers ai and bi,denoting
an edge between vertices ai and bi (1≤ai,bi≤n).
The sum of n is not bigger than 800000.

 

Output

For each test output one line contains a integer,denoting the maximum size of Bobo Set.

 

Sample Input

 

Sample Output

 

Source

2015 Multi-University Training Contest 3

#include <iostream>

#include <cstdio>

#include <cstring>

#include <vector>

#include <algorithm>

#pragma comment(linker, "/STACK:102400000,102400000")//手动扩栈

typedef long long ll;

using namespace std;

const int maxn= 5e5 + 5;

const ll INF = 1000000000000000000;

int p[maxn];

vector<int>q[maxn];

int num[maxn];

void dfs(int u)

{

    num[u]++;

    int len = q[u].size();

    for(int i = 0;i < len;i++)

    {

        int son = q[u][i];

        if(!num[son])

            dfs(son);

        num[u]+=num[son];

    }

}

int main()

{

    int n;

    //freopen("10.txt","r",stdin);

    while(scanf("%d",&n) != EOF)

    {

        for(int i = 1;i <= n;i++)

            scanf("%d",&p[i]);

        int a,b;

        for(int i = 1;i <= n;i++)

            q[i].clear();

        for(int i = 1;i < n;i++)

        {

            scanf("%d%d",&a,&b);

            if(p[a] < p[b])

                q[a].push_back(b);

            else

                q[b].push_back(a);

        }

        int ans = 0;

        memset(num,0,sizeof(num));

        for(int i = 1;i <= n;i++)

        {

            if(!num[i])

                dfs(i);

            ans= max(ans,num[i]);

        }

        printf("%d\n",ans);

    }

}