Update 315-count-of-smaller-numbers-after-self.js

Author: everthis

315-count-of-smaller-numbers-after-self.js

@@ -1,3 +1,46 @@
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+const countSmaller = function(nums) {
+  const numsAndIndexes = nums.map((x, i) => [x, i])
+  const output = [...new Array(nums.length)].map(_ => 0)
+  mergeSort(numsAndIndexes, output)
+  return output
+}
+
+function mergeSort(arr, output) {
+  if (arr.length <= 1) return arr
+  const middle = Math.floor(arr.length / 2)
+  const left = mergeSort(arr.slice(0, middle), output),
+    right = mergeSort(arr.slice(middle), output)
+  const sorted = []
+  let i = 0,
+    j = 0
+  while (i < left.length || j < right.length) {
+    if (i >= left.length) {
+      sorted.push(right[j])
+      j++
+    } else if (j >= right.length) {
+      sorted.push(left[i])
+      i++
+    } else {
+      if (left[i][0] > right[j][0]) {
+        sorted.push(left[i])
+        output[left[i][1]] += right.length - j
+        i++
+      } else {
+        sorted.push(right[j])
+        j++
+      }
+    }
+  }
+
+  return sorted
+}
+
+// another
+
 class Node {
   constructor(v, s) {
     this.val = v