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]

Classic divide and conquer.

public class Solution {
    public List<Integer> diffWaysToCompute(String input) {
        List<Integer> list  = new ArrayList<>();
        for(int i=0; i< input.length(); i++){
            if(Character.isDigit(input.charAt(i))) continue;
            List<Integer> l = diffWaysToCompute(input.substring(0, i));
            List<Integer> r = diffWaysToCompute(input.substring(i+1));
            for(Integer li : l){
                for(Integer ri : r){
                    switch (input.charAt(i)){
                        case '+':
                            list.add(li+ri);
                            break;
                        case '-':
                            list.add(li - ri);
                            break;
                        case '*':
                            list.add(li * ri);
                            break;
                        //throws
                    }
                }
            }
        }
        if(list.isEmpty()){
            list.add(Integer.parseInt(input));
        }
        return list;
    }
}