树状数组-实战一（洛谷P3368）

单点更新代码：

void add(int a , int b)
{
    while(a <= n)
    {
        tree[a] += b;
        a += lowbit(a);
    }
}

区间求和代码：

int sum(int x)
{
    int ans = 0;
    while(x != 0)
    {
        ans += tree[x];
        x -= lowbit(x);
    }
    return ans;
}

主代码：

#include<bits/stdc++.h>
using namespace std;
int n , m;
int tree[500001];
int lowbit(int k)
{
    return k & -k;
}
void add(int a , int b)
{
    while(a <= n)
    {
        tree[a] += b;
        a += lowbit(a);
    }
}
int sum(int x)
{
    int ans = 0;
    while(x != 0)
    {
        ans += tree[x];
        x -= lowbit(x);
    }
    return ans;
}
int main(void)
{
    int x ,y = 0 , z ,flag;
    int num;
    cin>>n>>m;
    for(int i = 1 ; i <= n ; i ++)
    {
        cin>>x;
        add(i,x-y);
        y = x;
    }
    for(int i = 1 ; i <= m ; i ++)
    {
        cin>>flag;
        if(flag == 1)
        {
            cin>>x>>y>>z;
            add(x,z);
            add(y+1,-z);
        }
        if(flag == 2)
        {
            cin>>x;
            cout<<sum(x)<<endl;
        }
    }
    return 0;
}

如有不懂参考如下：

https://blog.csdn.net/qq_33982232/article/details/81273634

https://blog.csdn.net/Small_Orange_glory/article/details/81290634