[LeetCode] Different Ways to Add Parentheses

Java Code:

public class Solution {
    public List<Integer> diffWaysToCompute(String input) {
        List<Integer> result = new ArrayList<Integer>();
        if (input == null || input.length() == 0) {
            return result;
        }
        
        for (int i = 0; i < input.length(); i++) {
            char c = input.charAt(i);
            if (c != '+' && c != '-' && c != '*') {
                continue;
            }
            
            List<Integer> part1Result = 
                diffWaysToCompute(input.substring(0, i));
            List<Integer> part2Result = 
                diffWaysToCompute(input.substring(i + 1, input.length()));
            
            for (Integer m : part1Result) {
                for (Integer n : part2Result) {
                    if (c == '+') {
                        result.add(m + n);
                    } else if (c == '-') {
                        result.add(m - n);
                    } else if (c == '*') {
                        result.add(m * n);
                    }
                }
            }
        }
        
        if (result.size() == 0) {
            result.add(Integer.parseInt(input));
        }
        
        return result;
    }
}

reference:
https://leetcode.com/discuss/48477/a-recursive-java-solution-284-ms