求助关于树状数组的

#include<iostream>
#include<cstdio>

using namespace std;

#define lowbit(i) i&-i
#define abs(x) x<0?x:0 
#define MAX 500005

int n,m,arr[MAX];
int sum(int x){
	int res=0;
	for(;x;x-=lowbit(x))
		res+=arr[x];
	return res;
}
void add(int x,int uvs){ 
	for(;x<=n;x+=lowbit(x))
		arr[x]+=uvs;
}
void work(){
	int p,x,y;
	cin>>n>>m;
	for(int i=1;i<=n;++i){
		cin>>x;
		add(i,x); 
	}	
	for(int i=1;i<=m;++i){
		cin>>p>>x>>y;
		if(p==1)
			add(x,y);
		if(p==2)
			cout<<sum(y)-sum(x-1)<<"\n"; 
	}
}
int main(){
	work(); 
	return 0;
}