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Problem

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

Example 2:

Input: "2*3-4*5"
Output: [-34, -14, -10, -10, 10]
Explanation:
(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

Code

class Solution {
    public List<Integer> diffWaysToCompute(String input) {
        if(input == null || input.length() == 0) return new ArrayList<>();

        List<Integer> res = new ArrayList<>();

        for(int i = 0; i < input.length(); i++) {
            char c = input.charAt(i);
            if(c == '+' || c == '-' || c == '*') {
                List<Integer> left = diffWaysToCompute(input.substring(0, i));
                List<Integer> right = diffWaysToCompute(input.substring(i + 1));

                for(int l : left) {
                    for(int r : right){
                        if(c == '+'){
                            res.add(l + r);
                        } else if (c == '-') {
                            res.add(l - r);
                        } else if (c == '*') {
                            res.add(l * r);
                        }
                    }
                }
            }
        }

        if(res.size() == 0){
            res.add(Integer.valueOf(input));
        }
        return res;
    }
}

class Solution:
    def diffWaysToCompute(self, input: str) -> List[int]:
        if not input:
            return []

        res = []
        for i in range(len(input)):
            c = input[i]

            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)
                        elif c == '-':
                            res.append(l - r)
                        elif c == '*':
                            res.append(l * r)

        if not res:
            res.append(int(input))
        return res