Leetcode-20: Valid Parentheses

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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: 括号匹配很简单，数据结构中教过大家使用栈来对括号进行匹配，左括号压栈，有对应的右括号出栈，否则返回false，最终的栈中为空即返回true，否则返回false。

public class Solution {    public boolean isValid(String s) {        Deque<Character> deque = new LinkedList<>();        for (int i = 0; i < s.length(); ++i) {            char c = s.charAt(i);            if ((c == '(') || (c == '[') || (c == '{'))                deque.addFirst(c);            else {                if (deque.isEmpty()) return false;                if (c == ')' && deque.getFirst() != '(' ||                    c == ']' && deque.getFirst() != '[' ||                    c == '}' && deque.getFirst() != '{')                    return false;                deque.removeFirst();                    }        }        return deque.isEmpty();                            }}

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