📦 NEW: Added Solution and Testcases for Project Euler Problem 24

Author: pomkarnath98

Project-Euler/Problem024.js

@@ -0,0 +1,21 @@
+function factorial(n) {
+  return n <= 1 ? 1 : n * factorial(n - 1)
+}
+
+export function findNthLexicographicPermutation(digits, n) {
+  let permutation = ''
+  let k = n - 1
+
+  while (digits.length > 0) {
+    const fact = factorial(digits.length - 1)
+    const index = Math.floor(k / fact)
+    permutation += digits[index]
+    digits.splice(index, 1)
+    k %= fact
+  }
+
+  return permutation
+}
+
+const digits = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+console.log(findNthLexicographicPermutation(digits, 1000000))

Project-Euler/test/Problem024.test.js

@@ -0,0 +1,31 @@
+import { describe, it, expect } from 'vitest'
+import { findNthLexicographicPermutation } from '../Problem024'
+
+describe('findNthLexicographicPermutation', () => {
+  it('should return the correct permutation for small cases', () => {
+    expect(findNthLexicographicPermutation([0, 1, 2], 1)).toBe('012')
+    expect(findNthLexicographicPermutation([0, 1, 2], 2)).toBe('021')
+    expect(findNthLexicographicPermutation([0, 1, 2], 6)).toBe('210')
+  })
+
+  it('should return the correct 1st permutation for digits 0-9', () => {
+    expect(
+      findNthLexicographicPermutation([0, 1, 2, 3, 4, 5, 6, 7, 8, 9], 1)
+    ).toBe('0123456789')
+  })
+
+  it('should return the correct millionth permutation for digits 0-9', () => {
+    expect(
+      findNthLexicographicPermutation([0, 1, 2, 3, 4, 5, 6, 7, 8, 9], 1000000)
+    ).toBe('2783915460')
+  })
+
+  it('should return the correct permutation for a smaller set of digits', () => {
+    expect(findNthLexicographicPermutation([1, 2, 3, 4], 12)).toBe('2431')
+    expect(findNthLexicographicPermutation([1, 2, 3, 4], 24)).toBe('4321')
+  })
+
+  it('should handle large values of n', () => {
+    expect(findNthLexicographicPermutation([0, 1, 2, 3, 4], 120)).toBe('43210')
+  })
+})