[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;    }