[LeetCode 241] 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]

solution:

Recursive to calculate left value and right value, then make combination.

public List<Integer> diffWaysToCompute(String input) {
        List<Integer> res = new ArrayList<>();
        for(int i=0;i<input.length();i++){
            char c = input.charAt(i);
            if('+' == c || '-' == c || '*' == c) {
                String lv = input.substring(0, i);
                String rv = input.substring(i+1);
                List<Integer> lefts = diffWaysToCompute(lv);
                List<Integer> rights = diffWaysToCompute(rv);
                for(int j : lefts) {
                    for(int k: rights){
                        int temp = 0;
                        switch(c){
                            case'+': 
                                temp = j+k;
                                break;
                            case'-': 
                                temp = j-k;
                                break;
                            case'*': temp = j*k;
                        }
                        res.add(temp);
                    }
                }
            }
        }
        if(res.isEmpty()){
                res.add(Integer.valueOf(input));
            }
        return res;
    }