字节跳动面试题：用归并排序判断冒泡排序的轮数

树状数组的讲解：

https://www.cnblogs.com/xenny/p/9739600.html

面试题的答案在此：

https://blog.youkuaiyun.com/优快云_Coder_T/article/details/77456548

http://www.manongjc.com/detail/11-italvzpqijcxbyu.html（这个清楚点）

我自己写的答案：

#include<iostream>
#include<vector>
using namespace std;

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

int sum(int i, vector<int>& c)
{
    int s = 0;
    while (i > 0)
    {
        s += c[i];
        i -= lowbit(i);
    }
    return s;
}

void add(int i, int val, vector<int>& c)
{
    int len = c.size();
    while (i < len)
    {
        c[i] += val;
        i += lowbit(i);
    }
}

int main()
{
    int b[] = {3,1,5,8,2};
    vector<int> v(b, b+5);
    vector<int> c(101, 0);
    int res = 0;
    for (int i = 0; i < v.size(); i++)
    {
        int num = v[i];
        res = max(res, i - sum(num, c));
        add(num, 1, c);
    }
    cout << res << endl;
    return 0;
}

leetcode上的树状数组题目：

493 翻转对

307 range sum