数组中的逆序对

使用归并排序，右边小的上去就可以知道前面有多少个比它大的了

public class Solution {
    int count = 0;
    public int InversePairs(int [] array) {
        if(array.length < 2)
            return 0;
        mergeSort(array,0,array.length-1);
        return count;
    }

    public void mergeSort(int[] array,int left,int right){
        int mid = left+(right-left)/2;
        if(left < right){
            mergeSort(array,left,mid);
            mergeSort(array,mid+1,right);
            merge(array,left,mid,right);
        }
    }

    public void merge(int[] array,int left,int mid,int right){
        int[] arr =  new int[right-left+1];
        int c = 0;
        int s = left;
        int l = left;       
        int r = mid+1;
        while(l <= mid && r <= right ){
            if(array[l] <= array[r]){
                arr[c] = array[l];
                c++;
                l++;
            }else{
                arr[c] = array[r];
                count += mid+1-l;
                count %= 1000000007;
                c++;
                r++;
            }
        }

        while(l <= mid)
            arr[c++] = array[l++];
        while(r <= right)
            arr[c++] = array[r++];
        for(int num:arr){
            array[s++] = num;
        }
    }
}