入门题

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 50010;
struct edge
{
	int v, next;
}e[maxn*2];

int n, m, q;

int first[maxn], cnt;
int top[maxn], tid[maxn], rank[maxn], sz[maxn], f[maxn], son[maxn], dep[maxn], tim;
int d[maxn][2], a[maxn];

void AddEdge(int u, int v)
{
	e[cnt].v = v;
	e[cnt].next = first[u];
	first[u] = cnt++;
	e[cnt].v = u;
	e[cnt].next = first[v];
	first[v] = cnt++;
}

void dfs1(int u, int fa, int d)
{
	sz[u] = 1;
	f[u] = fa;
	dep[u] = d;
	for(int i = first[u]; i != -1; i = e[i].next)
	{
		int v = e[i].v;
		if(v == f[u])
			continue;
		dfs1(v, u, d+1);
		sz[u] += sz[v];
		if(son[u] == -1 || sz[son[u]] < sz[v])
			son[u] = v;
	}
}

void dfs2(int u, int tp)
{
	top[u] = tp;
	tid[u] = ++tim;
	rank[tid[u]] = u;
	if(son[u] == -1)
		return;
	dfs2(son[u], tp);
	for(int i = first[u]; i != -1; i = e[i].next)
	{
		int v = e[i].v;
		if(v != son[u] && v != f[u])
			dfs2(v, v);
	}
}
void init()
{
	memset(first, -1, sizeof(first));
	cnt = 0;
	memset(son, -1, sizeof(son));
	tim = 0;
}


int st[maxn<<2];
int lz[maxn<<2];
void build(int l, int r, int rt)
{
	st[rt] = lz[rt] = 0;
	if(l == r)
	{
		lz[rt] = a[rank[l]];
		return;
	}
	int m = (l + r) >> 1;
	build(l, m, rt<<1);
	build(m+1, r, rt<<1|1);
}

void pushdown(int l, int r, int rt)
{
	if(lz[rt])
	{
		lz[rt<<1] += lz[rt];
		lz[rt<<1|1] += lz[rt];
		lz[rt] = 0;
	}
}
void update(int x, int y, int l, int r, int rt, int w)
{
	if(x == l && y == r)
	{
		lz[rt] += w;
		return;
	}
	pushdown(l, r, rt);
	int m = (l + r) >> 1;
	if(y <= m)
		update(x, y, l, m, rt<<1, w);
	else if(x > m)
		update(x, y, m+1, r, rt<<1|1, w);
	else
	{
		update(x, m, l, m, rt<<1, w);
		update(m+1, y, m+1, r, rt<<1|1, w);
	}
}

int query(int l, int r, int rt, int x)
{
	if(l == r)
		return lz[rt];
	pushdown(l, r, rt);
	
	int m = (l + r) >> 1;
	if(x <= m)
		return query(l, m, rt<<1, x);
	else
		return query(m+1, r, rt<<1|1, x);
}
void change(int u, int v, int w)
{
	while(top[u] != top[v])
	{
		if(dep[top[u]] < dep[top[v]])
			swap(u, v);
		update(tid[top[u]], tid[u], 1, n, 1, w);
		u = f[top[u]];
	}
	if(dep[u] > dep[v])
		swap(u, v);
	update(tid[u], tid[v], 1, n, 1, w);
}
int main()
{
	while(scanf("%d %d %d", &n, &m, &q) != EOF)
	{
		init();
		for(int i = 1; i <= n; i++)
			scanf("%d", &a[i]);
		for(int i = 1; i <= m; i++)
		{
			int u, v;
			scanf("%d %d", &u, &v);
			AddEdge(u, v);
		}
		dfs1(1, -1, 0);
		dfs2(1, 1);
		build(1, n, 1);
		while(q--)
		{
			char s[10];
			scanf("%s", s);
			if(s[0] == 'I')
			{
				int u, v, w;
				scanf("%d %d %d", &u, &v, &w);
				change(u, v, w);
			}
			else if(s[0] == 'D')
			{
				int u, v, w;
				scanf("%d %d %d", &u, &v, &w);
				change(u, v, -w);
			}
			else
			{
				int x;
				scanf("%d", &x);
				printf("%d\n", query(1, n, 1, tid[x]));
			}
		}
	}
	return 0;
}

HDU 3966 Aragorn's Story 树链剖分