leetcode - 2232. Minimize Result by Adding Parentheses to Expression

Description

You are given a 0-indexed string expression of the form “+” where and represent positive integers.

Add a pair of parentheses to expression such that after the addition of parentheses, expression is a valid mathematical expression and evaluates to the smallest possible value. The left parenthesis must be added to the left of ‘+’ and the right parenthesis must be added to the right of ‘+’.

Return expression after adding a pair of parentheses such that expression evaluates to the smallest possible value. If there are multiple answers that yield the same result, return any of them.

The input has been generated such that the original value of expression, and the value of expression after adding any pair of parentheses that meets the requirements fits within a signed 32-bit integer.

Example 1:

Input: expression = "247+38"
Output: "2(47+38)"
Explanation: The expression evaluates to 2 * (47 + 38) = 2 * 85 = 170.
Note that "2(4)7+38" is invalid because the right parenthesis must be to the right of the '+'.
It can be shown that 170 is the smallest possible value.

Example 2:

Input: expression = "12+34"
Output: "1(2+3)4"
Explanation: The expression evaluates to 1 * (2 + 3) * 4 = 1 * 5 * 4 = 20.

Example 3:

Input: expression = "999+999"
Output: "(999+999)"
Explanation: The expression evaluates to 999 + 999 = 1998.

Constraints:

3 <= expression.length <= 10
expression consists of digits from '1' to '9' and '+'.
expression starts and ends with digits.
expression contains exactly one '+'.
The original value of expression, and the value of expression after adding any pair of parentheses that meets the requirements fits within a signed 32-bit integer.

Solution

Try every possible position to put the parentheses.

Time complexity: $o(n^2)$
Space complexity: $o(1)$

Code

class Solution:
    def minimizeResult(self, expression: str) -> str:
        def get_value_from_expression(expression: str) -> int:
            left, right = expression.find('('), expression.find(')')
            res = eval(expression[left + 1: right])
            if left == 0 and right == len(expression) - 1:
                pass
            elif left == 0:
                res *= int(expression[right + 1:])
            elif right == len(expression) - 1:
                res *= int(expression[:left])
            else:
                res *= int(expression[:left]) * int(expression[right + 1:])
            return res

        left_index = []
        right_index = []
        add_index = expression.find('+')
        for i in range(len(expression)):
            if i < add_index:
                left_index.append(i)
            elif i > add_index:
                right_index.append(i + 1)
        min_val = float('inf')
        res = ''
        for l in left_index:
            for r in right_index:
                cur_expression = f'{expression[:l]}({expression[l:r]}){expression[r:]}'
                cur_value = get_value_from_expression(cur_expression)
                if cur_value < min_val:
                    min_val = cur_value
                    res = cur_expression
        return res