LeetCode-1003 Check If Word Is Valid After Substitutions Solution (with Java)

1. Description:

Notes:

2. Examples:

3.Solutions:

/**
 * Created by sheepcore on 2019-05-07
 */
class Solution {
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        for(char ch : s.toCharArray()){
            switch(ch){
                case 'a':
                case 'b': stack.push(ch); break;
                case 'c':
                    if(!stack.isEmpty() && stack.peek() == 'b')
                        stack.pop();
                    else
                        return false;
                    if(!stack.isEmpty() && stack.peek() == 'a')
                        stack.pop();
                    else
                        return false;
                    break;
            }
        }
        return stack.isEmpty(); 
    }
}