HDU5692 Snacks【dfs序】

題意：一棵樹，點上有權，從0出發，必須經過x，求最大點權和。可以修改某個點的權。

思路：可以轉化爲0到x的子樹裏的點的最大距離。dfs序求從0到x的距離，再建樹。修改某個點，相當於修改這個點子樹區間的值，區間更新。查詢，區間最大值。

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<stdio.h>
#include<iostream>
#include<string.h>
#include<string>
#include<stdlib.h>
#include<math.h>
#include<vector>
#include<list>
#include<map>
#include<set>
#include<stack>
#include<queue>
#include<algorithm>
#include<numeric>
#include<functional>
using namespace std;
#define lson(x) 2*x
#define rson(x) 2*x+1
typedef long long ll;
typedef pair<int,int> pii;
const int maxn = 100005;
int in[maxn],out[maxn];
struct Edge
{
	int to,next;
}edge[2*maxn];
int head[maxn],tot,t,vis[maxn];
ll b[maxn],a[maxn],num[maxn];

void init()
{
	memset(head,-1,sizeof head);
	memset(vis,0,sizeof vis);
	tot = 0;
	t = 0;
}

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

void dfs(int x,int fa)
{
	vis[x] = 1;
	in[x] = ++t;
	if(fa != -1)
		a[x] = a[x] + a[fa];
	num[t] = a[x];
	for(int i = head[x]; i != -1; i = edge[i].next)
	{
		int y = edge[i].to;
		if(vis[y]) continue;
		dfs(y,x);
	}
	out[x] = t;	
}

struct data
{
	int l,r;
	ll laz,num;
}node[maxn*4];

void pushup(int cnt)
{
	node[cnt].num = max(node[lson(cnt)].num,node[rson(cnt)].num);
}

void build(int x,int y, int cnt)
{
	node[cnt].l = x;
	node[cnt].r = y;
	node[cnt].laz = 0;
	if(x == y)
	{
		node[cnt].num = num[x];
		return;
	}
	int mid = (x+y) / 2;
	build(x,mid,lson(cnt));
	build(mid+1,y,rson(cnt));
	pushup(cnt);
}

void down(int cnt)
{
	if(node[cnt].laz == 0) return;
	ll tg = node[cnt].laz;
	node[lson(cnt)].laz += tg;
	node[rson(cnt)].laz += tg;
	node[lson(cnt)].num += tg;
	node[rson(cnt)].num += tg;
	node[cnt].laz = 0;
}

void up(int x,int y,int cnt,ll val)
{
	if(x == node[cnt].l && y == node[cnt].r)
	{
		node[cnt].laz += val;
		node[cnt].num += val;
		return;
	}
	down(cnt);
	int mid = (node[cnt].l + node[cnt].r) / 2;
	if(y <= mid)
		up(x,y,lson(cnt),val);
	else if(x >= mid+1)
		up(x,y,rson(cnt),val);
	else
	{
		up(x,mid,lson(cnt),val);
		up(mid+1,y,rson(cnt),val);
	}	
	pushup(cnt);
}

ll fid(int x,int y,int cnt)
{
	if(x == node[cnt].l && y == node[cnt].r)
	{
		return node[cnt].num;
	}
	down(cnt);
	int mid = (node[cnt].l + node[cnt].r) / 2;
	if(y <= mid)
		return fid(x,y,lson(cnt));
	else if(x >= mid+1)
		return fid(x,y,rson(cnt));
	else
		return max( fid(x,mid,lson(cnt)) , fid(mid+1,y,rson(cnt)));
}

int main(void)
{
	int n,T,m,kase = 1;
	scanf("%d",&T);
	while(T--)
	{
		scanf("%d%d",&n,&m);
		init();
		for(int i = 1; i < n; i++)
		{
			int x,y;
			scanf("%d%d",&x,&y);
			add(x,y);
			add(y,x);
		}
		for(int i = 0; i < n; i++)
		{
			scanf("%I64d",&b[i]);
			a[i] = b[i];
		}
		dfs(0,-1);
		build(1,n,1);
		printf("Case #%d:\n",kase++);
		while(m--)
		{
			int op,x;
			ll u;
			scanf("%d",&op);
			if(op == 0)
			{
				scanf("%d%I64d",&x,&u);
				up(in[x],out[x],1,u-b[x]);
				b[x] = u;
			}
			else
			{
				scanf("%d",&x);
				printf("%I64d\n",fid(in[x],out[x],1));
			}
		}
	}
	return 0;
}