树状数组

from ： acwing 

#include <bits/stdc++.h>
using namespace std;
const int N = 100001;
int n, m;
int tree[N], a[N];

int lowbit(int x){
    return x & -x;
}

void update(int x, int v){//这是下标x数加上v值
    for(int i = x; i <= n; i += lowbit(i)) tree[i] += v;
}

int query(int x){//求前缀和
    int res = 0;
    for(int i = x; i; i -= lowbit(i))
        res += tree[i];
    return res;
}
int main(){
    cin >> n >> m;
    for(int i = 1; i <= n; i ++ ) cin >> a[i];
    for(int i = 1; i <= n; i ++ ) update(i, a[i]);//这是初始化前缀和，不是以前那样
    
    int k, x, y;
    while(m -- ){
        cin >> k >> x >> y;
        if(k == 0){
            cout << query(y) - query(x - 1) << "\n";
        }else update(x, y);
    }
    
    return 0;
}