Submission #1477509

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Source Code Expand

// This amazing code is by Eric Sunli Chen.
#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <utility>
#include <vector>
using namespace std;
template<typename T> void get_int(T &x)
{
	char t=getchar();
	bool neg=false;
	x=0;
	for(; (t>'9'||t<'0')&&t!='-'; t=getchar());
	if(t=='-')neg=true,t=getchar();
	for(; t<='9'&&t>='0'; t=getchar())x=x*10+t-'0';
	if(neg)x=-x;
}
template<typename T> void print_int(T x)
{
	if(x<0)putchar('-'),x=-x;
	short a[20]= {},sz=0;
	while(x>0)a[sz++]=x%10,x/=10;
	if(sz==0)putchar('0');
	for(int i=sz-1; i>=0; i--)putchar('0'+a[i]);
}
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define get1(a) get_int(a)
#define get2(a,b) get1(a),get1(b)
#define get3(a,b,c) get1(a),get2(b,c)
#define printendl(a) print_int(a),puts("")
typedef long long LL;
typedef unsigned long long uLL;
typedef pair<LL,LL> pii;
const int inf=0x3f3f3f3f;
const LL Linf=1ll<<61;
const double pi=acos(-1.0);

vector<int> g[133333];
vector<pii> a[133333];

LL ub;
int n,v[133333];
void dfs(int x)
{
	if((int)g[x].size()==0)
	{
		a[x].pb(mp(v[x],v[x]));
		return;
	}
	
	int l=g[x][0],r=g[x][1],cur=0;
	dfs(l);dfs(r);
	for(int i=(int)a[l].size()-1;i>=0;i--)
	{
		while(cur<(int)a[r].size()&&a[r][cur].ff+a[l][i].ss>ub)cur++;
		if(cur<(int)a[r].size())
		{
			a[x].pb(mp(a[l][i].ff+v[x],a[r][cur].ss+v[x]));
			a[x].pb(mp(a[r][cur].ss+v[x],a[l][i].ff+v[x]));
		}
	}
	cur=0;
	for(int i=(int)a[r].size()-1;i>=0;i--)
	{
		while(cur<(int)a[l].size()&&a[l][cur].ff+a[r][i].ss>ub)cur++;
		if(cur<(int)a[l].size())
		{
			a[x].pb(mp(a[r][i].ff+v[x],a[l][cur].ss+v[x]));
			a[x].pb(mp(a[l][cur].ss+v[x],a[r][i].ff+v[x]));
		}
	}/**/
/*	for(int i=0;i<(int)a[l].size();i++)for(int j=0;j<a[r].size();j++)
	{
		if(a[l][i].ff+a[r][j].ss<=ub)a[x].pb(mp(a[l][i].ss+v[x],a[r][j].ff+v[x]));
		if(a[l][i].ss+a[r][j].ff<=ub)a[x].pb(mp(a[l][i].ff+v[x],a[r][j].ss+v[x]));
	}/**/
	sort(a[x].begin(),a[x].end());
	cur=0;
	for(int i=0;i<(int)a[x].size();i++)
	{
		if(i==0||a[x][cur-1].ff>a[x][i].ff||a[x][cur-1].ss>a[x][i].ss)
			a[x][cur++]=a[x][i];
	}
	a[x].resize(cur);
//	printf("x= %d\n",x);
//	for(int i=0;i<(int)a[x].size();i++)printf("pair= %d %d\n",a[x][i].ff,a[x][i].ss);
//	puts("");
}
bool check(LL x)
{
	ub=x;
	for(int i=1;i<=n;i++)
	{
		a[i].clear();
		a[i].swap(a[i]);
	}
	dfs(1);
	if(a[1].size()>0)return true;
	else return false;
}
int main()
{
	get1(n);
	for(int i=2,a;i<=n;i++)
	{
		get2(a,v[i]);
		g[a].pb(i);
	}
//	printf("check %d\n",check(15));
	LL l=-1,r=1ll<<40,mid;
	while(l<r-1)
	{
		mid=(l+r)>>1;
		if(check(mid))r=mid;
		else l=mid;
	}
	printendl(r);/**/
	return 0;
}

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