LeetCode-921 Minimum Add to Make Parentheses Valid Solution (with Java)

1. Description: 

Notes: 

2. Examples: 

3.Solutions:

/**
 * Created by sheepcore on 2019-05-07
 */
class Solution {
    public int minAddToMakeValid(String s) {
        Stack<Character> stack = new Stack<Character>();
        int addnum = 0;
        for(int i = 0; i < s.length(); i++){
            char ch = s.charAt(i);
            switch(ch){
                case '(': stack.push(ch); break;
                case ')':
                    if(!stack.isEmpty() && stack.peek() == '(')
                        stack.pop();
                    else
                        addnum += 1;
                    break;
                default:
                    System.out.println("Invalid Parentheses");
            }
        }
        return addnum + stack.size();
    }
}