241.Different Ways to Add Parentheses

Given a string of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. The valid operators are+,-and*.

Example 1

Input:"2-1-1".

((2-1)-1) = 0
(2-(1-1)) = 2
Output:[0, 2]

Example 2

Input:"2*3-4*5"

(2*(3-(4*5))) = -34
((2*3)-(4*5)) = -14
((2*(3-4))*5) = -10
(2*((3-4)*5)) = -10
(((2*3)-4)*5) = 10
Output:[-34, -14, -10, -10, 10]

class Solution(object):
    def diffWaysToCompute(self, input):
        """
        :type input: str
        :rtype: List[int]
        """
        mem = {}
        def calculate(expr):
            if expr in mem:
                return mem[expr]
            if expr.isdigit():
                return [int(expr)]
            res = []
            for i, c in enumerate(expr):
                if c in '*+-':
                    first = calculate(expr[:i])
                    second = calculate(expr[i+1:])
                    for j in first:
                        for k in second:
                            res.append(eval(str(j) + c + str(k)))
            mem[expr] = res
            return res
        return calculate(input)