private long operate(int val1, int val2, char op) {
        switch (op) {
            case '+':
                return val1 + val2;
            case '-':
                return val1 - val2;
            case '*':
                return val1 * val2;
        }
        throw new IllegalArgumentException();
    }
https://leetcode.com/problems/different-ways-to-add-parentheses/
src/com/interview/recursion/DifferentWaysToAddParentheses.java