树状数组解题

const int MAXN = 1000000;
int tree[MAXN];
class Solution {
public:
    inline int lowbit(int pos) {
        return pos & -pos;
    }
    void update(int pos) {
        while (pos <= MAXN) {
            tree[pos] += 1;
            pos += lowbit(pos);
        }
    }
    int query(int pos) {
        int ans = 0;
        while (pos > 0) {
            ans += tree[pos];
            pos -= lowbit(pos);
        }
        return ans;
    }
    int inversePairs(vector<int> nums) {
        size_t size = nums.size();
        int result = 0;
        for (int i = 0; i < size; i++) {
            update(nums[i] + 1);
            result += (i + 1 - query(nums[i]+1));
        }
        return result;
    }
};