【2022初春】【剑指offer】51. 数组中的逆序对

归并的思路是看懂了，但是写起来还是很迷茫

class Solution {
    int[] nums,tmp;
    public int reversePairs(int[] nums) {
        this.nums = nums;
        tmp = new int[nums.length];
        return manage(0,nums.length-1);
    }
    public int manage(int l,int r){
        if(l>=r) return 0;
        int m = (l+r)/2;
        int res = manage(l,m) + manage(m+1,r);
        int i=l, j=m+1;
        for(int k=l; k<=r; k++){
            tmp[k] = nums[k];
        }
        for(int k=l; k<=r; k++){
            if(i==m+1){
                nums[k] = tmp[j++];
            }else if(j==r+1||tmp[i]<=tmp[j]){
                nums[k] = tmp[i++];
            }else{
                nums[k] = tmp[j++];
                res += m+1-i;
            }
        }
        return res;
    }
}