Add solution #2121

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,758 LeetCode solutions in JavaScript
+# 1,759 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1624,6 +1624,7 @@
 2117|[Abbreviating the Product of a Range](./solutions/2117-abbreviating-the-product-of-a-range.js)|Hard|
 2119|[A Number After a Double Reversal](./solutions/2119-a-number-after-a-double-reversal.js)|Easy|
 2120|[Execution of All Suffix Instructions Staying in a Grid](./solutions/2120-execution-of-all-suffix-instructions-staying-in-a-grid.js)|Medium|
+2121|[Intervals Between Identical Elements](./solutions/2121-intervals-between-identical-elements.js)|Medium|
 2127|[Maximum Employees to Be Invited to a Meeting](./solutions/2127-maximum-employees-to-be-invited-to-a-meeting.js)|Hard|
 2129|[Capitalize the Title](./solutions/2129-capitalize-the-title.js)|Easy|
 2130|[Maximum Twin Sum of a Linked List](./solutions/2130-maximum-twin-sum-of-a-linked-list.js)|Medium|

solutions/2121-intervals-between-identical-elements.js

@@ -0,0 +1,48 @@
+/**
+ * 2121. Intervals Between Identical Elements
+ * https://leetcode.com/problems/intervals-between-identical-elements/
+ * Difficulty: Medium
+ *
+ * You are given a 0-indexed array of n integers arr.
+ *
+ * The interval between two elements in arr is defined as the absolute difference between their
+ * indices. More formally, the interval between arr[i] and arr[j] is |i - j|.
+ *
+ * Return an array intervals of length n where intervals[i] is the sum of intervals between arr[i]
+ * and each element in arr with the same value as arr[i].
+ *
+ * Note: |x| is the absolute value of x.
+ */
+
+/**
+ * @param {number[]} arr
+ * @return {number[]}
+ */
+var getDistances = function(arr) {
+  const valueIndices = new Map();
+  const result = new Array(arr.length).fill(0);
+
+  for (let i = 0; i < arr.length; i++) {
+    if (!valueIndices.has(arr[i])) {
+      valueIndices.set(arr[i], []);
+    }
+    valueIndices.get(arr[i]).push(i);
+  }
+
+  for (const indices of valueIndices.values()) {
+    let prefixSum = 0;
+    for (let i = 1; i < indices.length; i++) {
+      prefixSum += indices[i] - indices[0];
+    }
+
+    result[indices[0]] = prefixSum;
+
+    for (let i = 1; i < indices.length; i++) {
+      const diff = indices[i] - indices[i - 1];
+      prefixSum += diff * (i - (indices.length - i));
+      result[indices[i]] = prefixSum;
+    }
+  }
+
+  return result;
+};