20.Valid Parentheses

import java.util.HashMap;
import java.util.Map;
import java.util.Stack;

public class Solution {
    public boolean isValid(String s) {
        Stack<Character> characterStack = new Stack<>();
        int len = s.length();
        Map<Character, Character> map = new HashMap<>();
        map.put(')', '(');
        map.put(']', '[');
        map.put('}', '{');
        for(int i = 0; i < len; ++i) {
            if( characterStack.isEmpty()) {
                characterStack.push(s.charAt(i));
                continue;
            }
            Character c = s.charAt(i);
            Character t = characterStack.peek();
            if(t == map.get(c)) characterStack.pop();
            else characterStack.push(c);
        }
        return characterStack.isEmpty();
    }
//
//    public static void main(String[] args) {
//        Solution solution = new Solution();
//        System.out.println(solution.isValid("()"));
//    }
}