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]

class Solution {
public List<Integer> diffWaysToCompute(String input) {
List<Integer> result = new ArrayList<>();
for (int i = 0; i < input.length(); i++) {
if (isOperator(input.charAt(i))) {
char operator = input.charAt(i);
List<Integer> left = diffWaysToCompute(input.substring(0, i));
List<Integer> right = diffWaysToCompute(input.substring(i + 1));
for (int num1 : left) {
for (int num2 : right) {
result.add(calculate(num1, num2, operator));
}
}
}
}
if (result.size() == 0) {
result.add(Integer.valueOf(input));
}
return result;
}

public int calculate(int num1, int num2, char operator) {
int result = 0;
switch(operator) {
case '+' : result = num1 + num2;
break;

4000
case '-' : result = num1 - num2;
break;

case '*' : result = num1 * num2;
break;
}
return result;
}

public boolean isOperator(char c) {
if (c == '+' || c == '-' || c == '*')
return true;
return false;
}
}