LeetCode : Valid Parentheses [java]

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.

思路：使用堆栈存储，遇到配对就弹出，为空则恰好全部配对成功。

import java.util.Stack;

public class Solution {
    public boolean isValid(String s) {
		Stack<Character> stack = new Stack<>();
		for (int i = 0; i < s.length(); i++) {
			char ch = s.charAt(i);
			switch (ch) {
			case ')':
				if (!stack.isEmpty() && stack.peek() == '(') {
					stack.pop();
				} else {
					stack.push(ch);
				}
				break;
			case ']':
				if (!stack.isEmpty() && stack.peek() == '[') {
					stack.pop();
				} else {
					stack.push(ch);
				}
				break;
			case '}':
				if (!stack.isEmpty() && stack.peek() == '{') {
					stack.pop();
				} else {
					stack.push(ch);
				}
				break;
			default:
				stack.push(ch);
			}
		}
		return stack.isEmpty();
    }
}