c++用归并排序计算右侧小于当前元素个数_c++ 计算右侧小于当前元素的个数 归并排序

class Solution {
public:
    vector<int> countSmaller(vector<int>& nums) {
        vector<pair<int, int>> array(nums.size());
        count.resize(nums.size(), 0);
        for(int i=0; i<nums.size(); i++){
            array[i] = {i, nums[i]};
        }
        tmp.resize(nums.size());
        sort(array, 0, nums.size()-1);
        return count;
    }
    vector<pair<int, int>> tmp;
    vector<int> count;
    void sort(vector<pair<int, int>>& array, int lo, int hi){
        if(lo >= hi) return;
        int mid = (lo + hi) >> 1;
        sort(array, lo, mid);
        sort(array, mid+1, hi);
        merge(array, lo, mid, hi);
    }
    void merge(vector<pair<int, int>>& array, int lo, int mid, int hi){
        for(int i=lo; i<=hi; i++){
            tmp[i] = array[i];
        }
        int i = lo;
        int j = mid+1;
        for(int p=lo; p<=hi; p++){
            if(i == mid+1){
                array[p] = tmp[j++];
            }
            else if(j == hi+1){
                array[p] = tmp[i++];
                count[array[p].first] += j-mid-1;
            }
            else if(tmp[i].second > tmp[j].second){
                array[p] = tmp[j++];
            }
            else if(tmp[i].second <= tmp[j].second){
                array[p] = tmp[i++];
                count[array[p].first] += j-mid-1;
            }
        }
    }
};