Different Ways to Add Parentheses

Source

• leetcode: 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]

Java

public class Solution {
    public List<Integer> diffWaysToCompute(String input) {
        List<Integer> result  = new ArrayList<Integer>();
        for(int i=0; i<input.length(); i++){
            char c = input.charAt(i);
            if(c=='+' || c=='-' || c=='*'){
                List<Integer> leftpart = diffWaysToCompute(input.substring(0, i));
                List<Integer> rightpart = diffWaysToCompute(input.substring(i+1));

                for(int l: leftpart){
                    for(int r: rightpart){
                        int res=0;
                        switch (c){
                            case '+': res=l+r; break;
                            case '-': res=l-r; break;
                            case '*': res=l*r; break;
                        }
                        result.add(res);
                    }
                }
            }
        }
        //check when input is a single number without + - * sign, like 8
        if(result.size()==0){
            result.add(Integer.valueOf(input));
        }
        return result;
    }
}

Reference

Different Ways to Add Parentheses