Hashing: Missing Number

Author: jhonnymoreira

src/hashing/missing-number.ts

@@ -0,0 +1,12 @@
+export function missingNumber(nums: number[]): number {
+  const n = nums.length;
+
+  /**
+   * Partial sums
+   * @see https://en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E2%8B%AF#Partial_sums
+   */
+  const rangeSum = (n * (n + 1)) / 2;
+  const numsSum = nums.reduce((total, num) => total + num, 0);
+
+  return rangeSum - numsSum;
+}

tests/hashing/missing-number.test.ts

@@ -0,0 +1,20 @@
+import { missingNumber } from '@/hashing/missing-number.js';
+
+describe('Hashing: Missing Number', () => {
+  test.each([
+    {
+      nums: [3, 0, 1],
+      output: 2,
+    },
+    {
+      nums: [0, 1],
+      output: 2,
+    },
+    {
+      nums: [9, 6, 4, 2, 3, 5, 7, 0, 1],
+      output: 8,
+    },
+  ])('missingNumber($nums) === $output', ({ nums, output }) => {
+    expect(missingNumber(nums)).toStrictEqual(output);
+  });
+});