20. Valid Parentheses

难度: Easy

题目描述

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.
3. Every close bracket has a corresponding open bracket of the same type.

 

Example 1:

Input: s = "()"

Output: true

Example 2:

Input: s = "()[]{}"

Output: true

Example 3:

Input: s = "(]"

Output: false

Example 4:

Input: s = "([])"

Output: true

Example 5:

Input: s = "([)]"

Output: false

 

Constraints:

• 1 <= s.length <= 104
• s consists of parentheses only '()[]{}'.

解题思路

代码实现

解决方案

java

class Solution {
    public boolean isValid(String s) {

        LinkedList<Character> list = new LinkedList<>();

        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c == '(' || c == '{' || c == '[') {
                list.push(c);
            } else {
                if (list.isEmpty()) {
                    return false;
                }
                switch (c) {
                    case ')':

                        Character p = list.pop();
                        if (p == null || p != '(') {
                            return false;
                        }
                        break;

                    case '}':
                        p = list.pop();
                        if (p == null || p != '{') {
                            return false;
                        }
                        break;
                    case ']':
                        p = list.pop();
                        if (p == null || p != '[') {
                            return false;
                        }
                        break;
                }

            }
        }

        return list.isEmpty();

    }
}