chore(Javascript): single occurring element among duplicates (#969)

algorithms/JavaScript/README.md

@@ -3,6 +3,7 @@
 ## Arrays
 
 - [Counting Inversions](src/arrays/counting-inversions.js)
+- [Single Occurring Element](src/arrays/single-occurring-element.js)
 
 ## Linked Lists
 

algorithms/JavaScript/src/arrays/single-occurring-element.js

@@ -0,0 +1,18 @@
+// Problem: Given an array of integers,
+// every element appears twice except for one. Find that single one.
+// Space Complexity: O(1)
+// Time Complexity: O(n)
+
+function singleOccurringElement(arr) {
+  let result = 0;
+  for (const el of arr) {
+    result ^= el;
+  }
+  return result;
+}
+
+const arr = [2, 5, 7, 3, 1, 8, 8, 9, 4, 2, 7, 1, 4, 9, 5];
+console.log(singleOccurringElement(arr));
+
+// Input: [2, 5, 7, 3, 1, 8, 8, 9, 4, 2, 7, 1, 4, 9, 5]
+// Output: 3

algorithms/JavaScript/src/index.js

@@ -1,5 +1,6 @@
 // Arrays
 require('./arrays/counting-inversions');
+require('./arrays/single-occurring-element');
 
 // Linked Lists
 require('./linked-lists/singly');