Add solution #442

Author: JoshCrozier

README.md

@@ -54,6 +54,7 @@
 350|[Intersection of Two Arrays II](./0350-intersection-of-two-arrays-ii.js)|Easy|
 383|[Ransom Note](./0383-ransom-note.js)|Easy|
 387|[First Unique Character in a String](./0387-first-unique-character-in-a-string.js)|Easy|
+442|[Find All Duplicates in an Array](./0442-find-all-duplicates-in-an-array.js)|Medium|
 448|[Find All Numbers Disappeared in an Array](./0448-find-all-numbers-disappeared-in-an-array.js)|Easy|
 451|[Sort Characters By Frequency](./0451-sort-characters-by-frequency.js)|Medium|
 459|[Repeated Substring Pattern](./0459-repeated-substring-pattern.js)|Easy|

solutions/0442-find-all-duplicates-in-an-array.js

@@ -0,0 +1,31 @@
+/**
+ * 442. Find All Duplicates in an Array
+ * https://leetcode.com/problems/find-all-duplicates-in-an-array/
+ * Difficulty: Medium
+ *
+ * Given an integer array nums of length n where all the integers of nums
+ * are in the range [1, n] and each integer appears once or twice, return
+ * an array of all the integers that appears twice.
+ *
+ * You must write an algorithm that runs in O(n) time and uses only constant
+ * extra space.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+var findDuplicates = function(nums) {
+  const result = [];
+
+  nums.forEach((num, i) => {
+    const key = Math.abs(num) - 1;
+    if (nums[key] < 0) {
+      result.push(Math.abs(num));
+    } else {
+      nums[key] *= -1;
+    }
+  });
+
+  return result;
+};