一道树状数组的好题

感谢@JCarlson帮忙找题

代码:

#include<set>
#include<map>
#include<list>
#include<queue>
#include<stack>
#include<string>
#include<time.h>
#include<math.h>
#include<memory>
#include<vector>
#include<bitset>
#include<fstream>
#include<stdio.h>
#include<utility>
#include<sstream>
#include<string.h>
#include<iostream>
#include<stdlib.h>
#include<algorithm>
using namespace std;
int a[100005];
void change(int i,int x)
{
    for (;i<=50000;)
    {
        a[i]+=x;
        i+=i&(-i);
    }
}
int sum(int i)
{
    int ans=0;
    for (;i!=0;)
    {
        ans+=a[i];
        i^=(i&(-i));
    }
    return ans;
}
int main()
{
    #ifdef absi2011
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
    #endif
    int t;
    scanf("%d",&t);
    int zu;
    for (zu=0;zu<t;zu++)
    {
        printf("Case %d:\n",zu+1);
        int i;
        int n;
        scanf("%d",&n);
        memset(a,0,sizeof(a));
        for (i=0;i<n;i++)
        {
            int x;
            scanf("%d",&x);
            change(i+1,x);
        }
        for (;;)
        {
            static char b[105];
            scanf("%s",b);
            if (b[0]=='Q')
            {
                int l,r;
                scanf("%d%d",&l,&r);
                l--;
                printf("%d\n",sum(r)-sum(l));
            }
            else if (b[0]=='S')
            {
                int l,x;
                scanf("%d%d",&l,&x);
                change(l,-x);
            }
            else if (b[0]=='A')
            {
                int l,x;
                scanf("%d%d",&l,&x);
                change(l,x);
            }
            else
            {
                break;
            }
        }
    }
    return 0;
}