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"
Output: [0, 2]
Explanation: 
((2-1)-1) = 0 
(2-(1-1)) = 2

Example 2:

Input: "2*3-4*5"
Output: [-34, -14, -10, -10, 10]
Explanation: 
(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

class Solution {
    Map<String, List<Integer>> map = new HashMap<>();
    public List<Integer> diffWaysToCompute(String input) {
        if(map.containsKey(input)) return map.get(input);
        
        List<Integer> ret = new ArrayList<>();
        for (int i=0; i<input.length(); i++) {
            if (input.charAt(i) == '-' ||
                input.charAt(i) == '*' ||
                input.charAt(i) == '+' ) {
                String part1 = input.substring(0, i);
                String part2 = input.substring(i+1);
                List<Integer> part1Ret = diffWaysToCompute(part1);
                List<Integer> part2Ret = diffWaysToCompute(part2);
                for (Integer p1 :   part1Ret) {
                    for (Integer p2 :   part2Ret) {
                        int c = 0;
                        switch (input.charAt(i)) {
                            case '+': c = p1+p2;
                                break;
                            case '-': c = p1-p2;
                                break;
                            case '*': c = p1*p2;
                                break;
                        }
                        ret.add(c);
                    }
                }
            }
        }
        //意味着input此时是数字
        if (ret.size() == 0) {
            ret.add(Integer.valueOf(input));
        }
        //将ret和input添加到map中，如果有重复可以直接使用
        map.put(input, ret);
        return ret;
    }
}

https://leetcode.com/problems/different-ways-to-add-parentheses/discuss/66328/A-recursive-Java-solution-(284-ms)

https://leetcode.com/problems/different-ways-to-add-parentheses/discuss/151979/Java-Python-Recursion-with-Explanation