Valid Parentheses

题目：

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input
string is valid.
The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and
"([)]" are not.

解答：

public class Solution {

    private static final Map<Character, Character> map = new HashMap<Character, Character>() {{
        put('(', ')');
        put('{', '}');
        put('[', ']');
    }};

    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        for(Char c : s.toCharArray()) {
            if(map.contaisKey(c)) {
                stack.push(c);
            } else if(stack.isEmpty() || map.get(stack.pop()) != c) {
                return false;
            }
        }

        return stack.isEmpty();
    }

    public static void main(String[] args) {
        String s = "[{}]";
        System.out.println(isValid(s));
    }
}