diff --git a/notes/51. 数组中的逆序对.md b/notes/51. 数组中的逆序对.md
index 959857d9..de00a5fe 100644
--- a/notes/51. 数组中的逆序对.md	
+++ b/notes/51. 数组中的逆序对.md	
@@ -1,6 +1,6 @@
 # 51. 数组中的逆序对
 
-[NowCoder](https://www.nowcoder.com/practice/96bd6684e04a44eb80e6a68efc0ec6c5?tpId=13&tqId=11188&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[Leetcode](https://leetcode.cn/problems/shu-zu-zhong-de-ni-xu-dui-lcof/)
 
 ## 题目描述
 
@@ -9,13 +9,17 @@
 ## 解题思路
 
 ```java
-private long cnt = 0;
-private int[] tmp;  // 在这里声明辅助数组，而不是在 merge() 递归函数中声明
+private int cnt = 0;
+private int[] tmp;
 
-public int InversePairs(int[] nums) {
-    tmp = new int[nums.length];
-    mergeSort(nums, 0, nums.length - 1);
-    return (int) (cnt % 1000000007);
+public int reversePairs(int[] record) {
+    if (record == null || record.length < 2) {
+        return 0;
+    }
+    this.cnt = 0;
+    this.tmp = new int[record.length];
+    mergeSort(record, 0, record.length - 1);
+    return cnt;
 }
 
 private void mergeSort(int[] nums, int l, int h) {