From 1b9c17c1590111e22cdef8be437db383a8fda2fe Mon Sep 17 00:00:00 2001
From: sarthakgupta1907-cell <sarthakgupta1907@gmail.com>
Date: Sat, 7 Nov 2026 10:46:27 +0530
Subject: [PATCH] feat: add bounce number algorithm

---
 Maths/BounceNumber.js           | 28 ++++++++++++++++++
 Maths/test/BounceNumber.test.js | 51 +++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 Maths/BounceNumber.js
 create mode 100644 Maths/test/BounceNumber.test.js

diff --git a/Maths/BounceNumber.js b/Maths/BounceNumber.js
new file mode 100644
index 0000000000..9a6ef75f61
--- /dev/null
+++ b/Maths/BounceNumber.js
@@ -0,0 +1,28 @@
+/**
+ * @function isBounceNumber
+ * @description A bounce number is a number whose digits are neither
+ *   entirely increasing nor entirely decreasing from left to right.
+ *   For example, 155349 is a bounce number.
+ * @param {number} n - A positive integer
+ * @returns {boolean} - True if n is a bounce number, false otherwise
+ * @see https://projecteuler.net/problem=112
+ * @example isBounceNumber(155349) => true
+ * @example isBounceNumber(1234) => false
+ * @example isBounceNumber(9876) => false
+ */
+const isBounceNumber = (n) => {
+  if (!Number.isInteger(n) || n < 1) {
+    throw new TypeError('Input must be a positive integer')
+  }
+  const digits = String(n).split('').map(Number)
+  if (digits.length === 1) return false
+  let increasing = false
+  let decreasing = false
+  for (let i = 1; i < digits.length; i++) {
+    if (digits[i] > digits[i - 1]) increasing = true
+    if (digits[i] < digits[i - 1]) decreasing = true
+  }
+  return increasing && decreasing
+}
+
+export { isBounceNumber }
diff --git a/Maths/test/BounceNumber.test.js b/Maths/test/BounceNumber.test.js
new file mode 100644
index 0000000000..6ced25e65f
--- /dev/null
+++ b/Maths/test/BounceNumber.test.js
@@ -0,0 +1,51 @@
+import { isBounceNumber } from '../BounceNumber.js'
+
+describe('isBounceNumber', () => {
+  test('155349 is a bounce number', () => {
+    expect(isBounceNumber(155349)).toBe(true)
+  })
+
+  test('121 is a bounce number', () => {
+    expect(isBounceNumber(121)).toBe(true)
+  })
+
+  test('1234 is NOT a bounce number (increasing)', () => {
+    expect(isBounceNumber(1234)).toBe(false)
+  })
+
+  test('9876 is NOT a bounce number (decreasing)', () => {
+    expect(isBounceNumber(9876)).toBe(false)
+  })
+
+  test('1111 is NOT a bounce number (all same)', () => {
+    expect(isBounceNumber(1111)).toBe(false)
+  })
+
+  test('single digit is NOT a bounce number', () => {
+    expect(isBounceNumber(5)).toBe(false)
+  })
+
+  test('132 is a bounce number', () => {
+    expect(isBounceNumber(132)).toBe(true)
+  })
+
+  test('321 is NOT a bounce number (decreasing)', () => {
+    expect(isBounceNumber(321)).toBe(false)
+  })
+
+  test('123454321 is a bounce number', () => {
+    expect(isBounceNumber(123454321)).toBe(true)
+  })
+
+  test('throws TypeError for zero', () => {
+    expect(() => isBounceNumber(0)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for negative input', () => {
+    expect(() => isBounceNumber(-121)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for float input', () => {
+    expect(() => isBounceNumber(1.5)).toThrow(TypeError)
+  })
+})