241. Different Ways to Add Parentheses java solutions

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.

public class Solution {
    public List<Integer> diffWaysToCompute(String input) {
        List<Integer> ans = new ArrayList<Integer>();
        for(int i = 0; i < input.length(); i++){
            char c = input.charAt(i);
            if(c != '+' && c != '-' && c != '*') continue;
            List<Integer> left = diffWaysToCompute(input.substring(0,i));
            List<Integer> right = diffWaysToCompute(input.substring(i+1,input.length()));
            for(int le : left){
                for(int ri : right){
                    if(c == '+') ans.add(le+ri);
                    else if(c == '-') ans.add(le-ri);
                    else if(c == '*') ans.add(le*ri);
                }
            }
        }
        if(ans.size() == 0) ans.add(Integer.parseInt(input));
        return ans;
    }
}

使用分治的思想。