[HDU 1166] 敌兵布阵

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1166

一个线段树区间求和的模板题了。

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;

#define MID(l,r) (l+r)>>1
#define lson root<<1
#define rson root<<1|1

const int maxn=5e4+5;
struct Tree
{
    int l,r;
    int sum;
}tree[maxn*3];

int arr[maxn],ans;

void Build(int root,int l,int r)
{
    tree[root].l=l;
    tree[root].r=r;
    if(l==r)
        tree[root].sum=arr[l];
    else
    {
        int mid=MID(l,r);
        Build(lson,l,mid);
        Build(rson,mid+1,r);
        tree[root].sum=tree[lson].sum+tree[rson].sum;
    }
}

void Query(int root,int x,int y)
{
    if(x<=tree[root].l&&y>=tree[root].r)
        ans+=tree[root].sum;
    else
    {
        int mid=MID(tree[root].l,tree[root].r);
        if(x>mid)
        {
            Query(rson,x,y);
        }
        else if(y<=mid)
        {
            Query(lson,x,y);
        }
        else
        {
            Query(lson,x,y);
            Query(rson,x,y);
        }
    }
}

void Update(int root,int x,int y)
{
    tree[root].sum+=y;
    if(tree[root].l==x&&tree[root].r==x)
        return ;
    int mid=MID(tree[root].l,tree[root].r);
    if(x>mid)
        Update(rson,x,y);
    else
        Update(lson,x,y);

}

int main()
{
    int T;
    cin>>T;
    for(int flag=1;flag<=T;flag++)
    {
        int n;
        cin>>n;
        for(int i=1;i<=n;i++)
            scanf("%d",&arr[i]);
        Build(1,1,n);
        printf("Case %d:
",flag);
        char s[10];
        while(scanf("%s",s)!=EOF)
        {
            if(strcmp(s,"End")==0)
                break;
            else if(strcmp(s,"Add")==0)
            {
                int x,y;
                scanf("%d%d",&x,&y);
                Update(1,x,y);
            }
            else if(strcmp(s,"Sub")==0)
            {
                int x,y;
                scanf("%d%d",&x,&y);
                Update(1,x,-y);
            }
            else if(strcmp(s,"Query")==0)
            {
                int x,y;
                scanf("%d%d",&x,&y);
                ans=0;
                Query(1,x,y);
                printf("%d
",ans);
            }
        }
    }
    return 0;
}