241. Different Ways to Add Parentheses

 1     public List<Integer> diffWaysToCompute(String input) {
 2         List<Integer> res = new ArrayList<Integer>();
 3         if(input == null || input.length() == 0) {
 4             return res;
 5         }
 6         for(int i = 0; i < input.length(); i++) {
 7             char x = input.charAt(i);
 8             if(x == ‘+‘ || x == ‘-‘ || x == ‘*‘) {
 9                 List<Integer> left = diffWaysToCompute(input.substring(0,i));
10                 List<Integer> right = diffWaysToCompute(input.substring(i+1));
11                 for(int eachLeft: left) {
12                     for(int eachRight: right) {
13                         if(x == ‘+‘) {
14                             res.add(eachLeft + eachRight);
15                         } else if(x == ‘-‘) {
16                             res.add(eachLeft - eachRight);
17                         } else {
18                             res.add(eachLeft * eachRight);
19                         }
20                     }
21                 }
22             }
23         }
24         if(res.isEmpty()) {
25             res.add(Integer.valueOf(input));
26         }
27         return res;
28     }