Factorial

Difficulty: Easy · Topic: Recursion

Return n! = n × (n-1) × ... × 1, with 0! = 1. You may write it recursively or iteratively, but think about the base case.

Examples

factorial(0)
→ 1

The empty product is 1.

factorial(1)
→ 1

factorial(5)
→ 120

5 × 4 × 3 × 2 × 1.

Target complexity: time O(n), space O(n)

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