For an array A, if i < j, and A [i] > A [j], called (A [i], A [j]) is a reverse pair.
return total of reverse pairs in A.

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Yes

Example

Given A =[2, 4, 1, 3, 5],(2, 1), (4, 1), (4, 3)are reverse pairs. return3

1. naive way. for loop

public class Solution {
    /**
     * @param A an array
     * @return total of reverse pairs
     */
    public long reversePairs(int[] A) {
        // Write your code here

        if (A == null || A.length < 2) {
            return 0;
        }
        int count = 0;
        for (int i = 0; i < A.length - 1; i++) {
            for (int j = i + 1; j < A.length; j++) {
                if (A[i] > A[j]) {
                    count++;
                }
            }
        }

        return count;

    }
}