[Leetcode] Clumsy Factorial (#1006)

 

 

문제 

 

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.

We make a clumsy factorial using the integers in decreasing order by swapping out the multiply operations for a fixed rotation of operations with multiply '*', divide '/', add '+', and subtract '-' in this order.

• For example, clumsy(10) = 10 * 9 / 8 + 7 - 6 * 5 / 4 + 3 - 2 * 1.

However, these operations are still applied using the usual order of operations of arithmetic. We do all multiplication and division steps before any addition or subtraction steps, and multiplication and division steps are processed left to right.

Additionally, the division that we use is floor division such that 10 * 9 / 8 = 90 / 8 = 11.

Given an integer n, return the clumsy factorial of n.

 

 

Example 1:

Input: n = 4
Output: 7
Explanation: 7 = 4 * 3 / 2 + 1

Example 2:

Input: n = 10
Output: 12
Explanation: 12 = 10 * 9 / 8 + 7 - 6 * 5 / 4 + 3 - 2 * 1

 

 

해설 코드 

class Solution:
    def clumsy(self, n):
        res = ""
        j = -1
        for i in range(n,0,-1):
            res += str(i)
            j += 1
            if j < n - 1:
                if j % 4 == 0:
                    res += "*"
                if j % 4 == 1:
                    res += "//"
                if j % 4 == 2:
                    res += "+"
                if j % 4 == 3:
                    res += "-"
        return eval(res)

분석 > 어려운 문제는 아니었는데 혼자 너무 꼬아서 생각했던 것 같다. n까지의 숫자를 거꾸로 하나씩 추가하면서 인덱스를 나타내는 j의 크기에 따라 부호를 추가하고 마지막에 eval 내장함수를 사용해 수식으로 계산하면 되었다. eval 이라는 편리한 내장함수를 이제야 알게 되었다니 ... 

 

 

 

Clumsy Factorial - LeetCode