线段树的一般模板，1.结构体数组tree来存储  2.线段树的构建函数buildTree  3.改变元素值函数update   4.查询区间内总和的函数query

全部使用递归来实现

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#include<iostream>
#include<stdio.h>
#include<string>
#include<string.h>

using namespace std;

const int maxn = 50050;
int ans;

struct node{
	int left, right, sum;
	int mid(){
		return (left+right)/2;
	}
}tree[maxn*4];

void buildTree(int left, int right, int rt)
{
	tree[rt].left = left;
	tree[rt].right = right;
	if(left == right){
		cin >> tree[rt].sum;
		return ;
	}
	int mid = tree[rt].mid();
	buildTree(left, mid, rt*2);
	buildTree(mid+1, right, rt*2+1);
	tree[rt].sum = tree[rt*2].sum + tree[rt*2+1].sum;
}

void query(int left, int right, int rt, int L, int R)
{
	if(L <= left && R >= right){
		ans += tree[rt].sum;
		return ;
	}
	int mid = tree[rt].mid();
	if(R <= mid)
		query(left, mid, rt*2, L, R);
	else if(L > mid)
		query(mid+1, right, rt*2+1, L, R);
	else
	{
		query(left, mid, rt*2, L, R);
		query(mid+1, right, rt*2+1, L, R);
	}
}

void update(int left, int right, int rt, int pos, int add)
{
	if(left == right)
	{
		tree[rt].sum += add;
		return ;
	}
	int mid = tree[rt].mid();
	if(pos <= mid)
		update(left, mid, rt*2, pos, add);
	else 
		update(mid+1, right, rt*2+1, pos, add);
	tree[rt].sum = tree[rt*2].sum + tree[rt*2+1].sum;
}

int main()
{
	int T, N, temp;
	int a, b, Case = 0;
	string str;
	scanf("%d",&T);
	while(T --)
	{
		cin >> N;
		buildTree(1, N, 1);
		Case ++;
		printf("Case %d:\n",Case);
		while( cin >> str )
		{
			if(str == "End") break;
			scanf("%d%d", &a, &b);
			if(str == "Add"){
				update(1, N, 1, a, b);
			}
			else if(str == "Sub"){
				update(1, N, 1, a, -b);
			}
			else {
				ans = 0;
				query(1, N, 1, a, b);
				printf("%d\n",ans); 
			}
		}
	}
	return 0;
}

hdu 1166线段树