hdu 1166 敌兵布阵（线段树单点更新，区间查询）

题意：区间和

思路：线段树

#include<iostream>
#include<stdio.h>
using namespace std;

#define MAXN 50005
int ans;

struct node{
    int left,right,sum;
    int mid(){
        return (left+right)>>;
    }
}tree[MAXN*];//注意范围，4倍空间

void btree(int left,int right,int rt){//建树
    tree[rt].left=left;
    tree[rt].right=right;
    if(left==right){
        scanf("%d",&tree[rt].sum);
        return;
    }
    int mid=tree[rt].mid();
    btree(left,mid,rt<<);
    btree(mid+,right,rt<<|);
    tree[rt].sum=tree[rt<<].sum+tree[rt<<|].sum;//区间里的点数=左区间+右区间
}

void query(int left,int right,int rt,int L,int R){//询问求和
    if(L<=left&&right<=R){
        ans+=tree[rt].sum;
        return;
    }
    int mid=tree[rt].mid();
    if(R<=mid)query(left,mid,rt<<,L,R);//区间在左子树
    else if(L>mid)query(mid+,right,rt<<|,L,R);//区间在右子树
    else{
        query(left,mid,rt<<,L,R);
        query(mid+,right,rt<<|,L,R);
    }
}

void update(int left,int right,int rt,int pos,int add){//单点更新函数
    if(left==right){
        tree[rt].sum+=add;
        return;
    }
    int mid=tree[rt].mid();
    if(pos<=mid)update(left,mid,rt<<,pos,add);//点在左子树
    else update(mid+,right,rt<<|,pos,add);//点在右子树
    tree[rt].sum=tree[rt<<].sum+tree[rt<<|].sum;//区间和更新
}

int main(){
    int t,n,a,b,i;
    char str[];
    scanf("%d",&t);
    for(i=;i<=t;++i){
        printf("Case %d:\n",i);
        scanf("%d",&n);
        btree(,n,);
        while(~scanf("%s",str)&&str[]!='E'){
            scanf("%d%d",&a,&b);
            if(str[]=='A')update(,n,,a,b);
            else if(str[]=='S')update(,n,,a,-b);
            else{
                ans=;
                query(,n,,a,b);
                printf("%d\n",ans);
            }
        }
    }
    return ;
}