Coding problem · Easy · Basics

Factorial

Easy Algorithms & data structures

Return n! (n factorial), the product of all integers from 1 to n. By definition 0! = 1. 0 <= n <= 18.

Example 1

Input: n = 5
Output: 120

Example 2

Input: n = 0
Output: 1

Hints

Hint 1

Multiply a running product by every number from 2 to n.

Hint 2

Recursion also works: n! = n × (n − 1)!

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Solution and explanation

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Time O(n) · Space O(1)

Iterate from 2 to n multiplying an accumulator that starts at 1. Factorials grow fast: 18! is about 6.4 × 10¹⁵, close to the largest integer JavaScript numbers represent exactly; Java uses long.

Reference solution

function factorial(n) {
  let result = 1;
  for (let i = 2; i <= n; i++) result *= i;
  return result;
}

function factorial(n: number): number {
  let result = 1;
  for (let i = 2; i <= n; i++) result *= i;
  return result;
}

def factorial(n: int) -> int:
    result = 1
    for i in range(2, n + 1):
        result *= i
    return result

<?php

function factorial(int $n): int
{
    $result = 1;
    for ($i = 2; $i <= $n; $i++) {
        $result *= $i;
    }
    return $result;
}

class Solution {
    public long factorial(int n) {
        long result = 1;
        for (int i = 2; i <= n; i++) result *= i;
        return result;
    }
}

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