241.md

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]

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

my thoughts:

1. peeked answer. recursion

my solution:

********** 72ms
class Solution:
    def diffWaysToCompute(self, input):
        """
        :type input: str
        :rtype: List[int]
        """
        if not input:
            return []
        res = []
        for i,c in enumerate(input):
            if c in '+-*':
                left = self.diffWaysToCompute(input[:i])
                right = self.diffWaysToCompute(input[i+1:])
                for l in left:
                    for r in right:
                        if c == '+':
                            res.append(l + r)
                        if c == '-':
                            res.append(l - r)
                        if c == '*':
                            res.append(l * r)
        if not res:
            return [int(input)]
        else:
            return sorted(res)
			
********** 44ms with memorization
class Solution:
    def __init__(self):
        self.d = {}
    def diffWaysToCompute(self, input):
        """
        :type input: str
        :rtype: List[int]
        """
        if not input:
            return []
        if input in self.d:
            return self.d[input]
        res = []
        for i,c in enumerate(input):
            if c in '+-*':
                left = self.diffWaysToCompute(input[:i])
                right = self.diffWaysToCompute(input[i+1:])
                for l in left:
                    for r in right:
                        if c == '+':
                            res.append(l + r)
                        if c == '-':
                            res.append(l - r)
                        if c == '*':
                            res.append(l * r)
        if not res:
            self.d[input] = [int(input)]
            return [int(input)]
        else:
            self.d[input] = sorted(res)
            return sorted(res)

my comments:

from other ppl's solution:

1. N/A