题解 | #数组中的逆序对#

public class Solution {
    
    private int re = 0;
    
    public int InversePairs(int [] array) {
        merge(array,0,array.length-1);
        return re;
    }
    
    public void merge(int[] array,int s,int e){
        if(s>=e){
            return;
        }
        int c = (s+e)>>1;
        merge(array,s,c);
        merge(array,c+1,e);
        int[] temp = new int[e-s+1];
        int i = 0;
        int r = c+1;
        int t = s;
        while(s<=c && r<=e){
            if(array[s]<=array[r]){
                temp[i++] = array[s++];
            }else{
                re = (re + c - s + 1)%1000000007;
                temp[i++] = array[r++];
            }
        }
        while(s<=c){
            temp[i++] = array[s++];
        }
        while(r<=e){
            temp[i++] = array[r++];
        }
        for (int value : temp) {
            array[t++] = value;
        }
    }
}