Create 493-reverse-pairs.js

Author: everthis

493-reverse-pairs.js

@@ -0,0 +1,25 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+const reversePairs = function(nums) {
+  return mergeSort(nums, 0, nums.length - 1);
+};
+
+function mergeSort(nums, s, e) {
+  if (s >= e) return 0;
+  let mid = s + Math.floor((e - s) / 2);
+  let cnt = mergeSort(nums, s, mid) + mergeSort(nums, mid + 1, e);
+  for (let i = s, j = mid + 1; i <= mid; i++) {
+    while (j <= e && nums[i] / 2.0 > nums[j]) j++;
+    cnt += j - (mid + 1);
+  }
+  sortSubArr(nums, s, e + 1);
+  return cnt;
+}
+
+function sortSubArr(arr, s, e) {
+  const tmp = arr.slice(s, e);
+  tmp.sort((a, b) => a - b);
+  arr.splice(s, e - s, ...tmp);
+}