Clumsy Factorial — LeetCode 1006 Python Solution

The problem

The factorial of a positive integer n is the product of all positive integers less than or equal to n. For example, factorial(10) = 10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1.

Example

Input

n = 4

Output

7

Explanation

7 = 4 * 3 / 2 + 1

Python solution

class Solution:
    def clumsy(self, n: int) -> int:
        k = 0
        stk = [n]
        for x in range(n - 1, 0, -1):
            if k == 0:
                stk.append(stk.pop() * x)
            elif k == 1:
                stk.append(int(stk.pop() / x))
            elif k == 2:
                stk.append(x)
            else:
                stk.append(-x)
            k = (k + 1) % 4
        return sum(stk)

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 1006. Clumsy Factorial is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Stack.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

Related problems