LeetCode:Different Ways to Add Parentheses

Different Ways to Add Parentheses

Total Accepted: 22360  Total Submissions: 62962  Difficulty: Medium

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.

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java code:

public class Solution {
    public List<Integer> diffWaysToCompute(String input) {
        List<Integer> ret = new ArrayList<Integer>();
        
        for(int i=0;i<input.length();i++){
            int c = input.charAt(i);
            
            if(c=='+' || c=='-' || c=='*') {
                List<Integer> leftList = diffWaysToCompute(input.substring(0,i));
                List<Integer> rightList = diffWaysToCompute(input.substring(i+1));
                for(int left : leftList){
                    for(int right : rightList){
                        int t = 0;
                        switch(c){
                            case '+': t = left + right;
                                break;
                            case '-': t = left - right;
                                break;
                            case '*': t = left * right;
                                break;
                        }
                        ret.add(t);
                    }
                }
            }
        }
        if(ret.size()==0){
            ret.add(Integer.valueOf(input));
        }
        return ret;
    }
}