Valid Parentheses

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本文介绍了一种使用堆栈数据结构来验证字符串中的括号是否正确配对的方法。具体实现包括如何处理圆括号、方括号及花括号等常见括号类型。

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.

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这道题目比较简单，用堆栈来处理，当遇到‘(’, ‘{’, ‘[’ 时就push到堆栈中，当遇到‘)’, ‘}’, ‘]’时，首先判断堆栈是否为空，如果为空说明之前字符中没有与right braces匹配的，返回false；如果堆栈不为空，判断是否匹配，如果匹配就继续往下匹配，如果不匹配直接返回false；最后要检查堆栈是否为空。代码如下：


public class Solution {
    public boolean isValid(String s) {
        if(s == null || s.length() == 0) return true;
        Stack<Character> stack = new Stack<Character>();
        for(int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if(c == '(' || c == '[' || c == '{') {
                stack.push(c);
            } else {
                if(stack.isEmpty()) return false;
                char tem = stack.pop();
                if(c == ')' && tem == '(') continue;
                if(c == '}' && tem == '{') continue;
                if(c == ']' && tem == '[') continue;
                return false; 
            }
        }
        return stack.isEmpty() == true;
    }
}