線段樹模板

#include<cstdio>
#include<algorithm>
using namespace std;
#define L o<<1
#define R (o<<1)|1
struct Node
{
	int l,r,sum,Max,Min;
}Tree[1000<<2];
void PushUp(int o)
{
	Tree[o].sum = Tree[o*2].sum + Tree[o*2+1].sum;
	Tree[o].Max = max(Tree[o*2].Max,Tree[o*2+1].Max);
	Tree[o].Min = min(Tree[o*2].Min,Tree[o*2+1].Min);
}
void Build(int o,int l,int r)
{
	//首先記錄l和r的值 
	Tree[o].l = l;
	Tree[o].r = r;
	if (l == r)		//到達最底層，遞歸終止
	{
		int t;
		scanf ("%d",&t);		//輸入數據 
		Tree[o].sum = Tree[o].Max = Tree[o].Min = t;		//更新節點數據 
		return;
	}
	int mid = (l+r) >> 1;		//找到中間節點 
	Build(o*2 , l , mid);		//遞歸建左子樹 
	Build(o*2+1 , mid+1 , r);		//遞歸建右子樹 
	PushUp(o);		//更新當前節點的值 
}
void UpDate(int o,int l,int r,int x,int y)		//把x節點更新爲y
{
	if (l == r)		//遞歸結束
	{
		Tree[o].Max = Tree[o].Min = Tree[o].sum = y;		//精確找到了節點，更新 
		return;
	}
	int mid = (l+r) / 2;		//找到中間位置
	if (x <= mid)
		UpDate(o*2,l,mid,x,y);		//找左子樹 
	else
		UpDate(o*2+1,mid+1,r,x,y);		//找右子樹 
	PushUp(o);		//更新當前節點 
}
int QuerySum(int o,int l,int r,int x,int y)		//查找x到y的和 
{
	if (l == x && r == y)		//如果恰好是當前節點，就返回 
	{
		return Tree[o].sum;
	}
	int mid = (l + r) / 2;
	if (mid >= y)		//全在左邊 
		return QuerySum(o*2,l,mid,x,y);
	else if (x > mid)		//全在右邊 
		return QuerySum(o*2+1,mid+1,r,x,y);
	else		//一半在左一半在右 
		return QuerySum(o*2,l,mid,x,mid) + QuerySum(o*2+1,mid+1,r,mid+1,y);
}
int main()
{
	int n;
	scanf ("%d",&n);
	Build(1,1,n);
//	UpDate(1,1,n,2,7);
	printf ("%d\n",QuerySum(1,1,n,2,4));
	return 0;
}