LeetCode之Valid Parentheses

1、题目

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.

 

2、思路

用stack来实现，左边的进栈，如果是右边的出栈，发现没有或者不匹配就返回false

 

 

 

 

 

 

3、代码实现

public class Solution {
    public boolean isValid(String s) {
        if (s == null || s.length() == 0) {
        return false;
        }
        char chars[] = s.toCharArray();
        Stack<Character> stack = new Stack<Character>();
        for (int i = 0; i < chars.length; ++i) {
        if (chars[i] == '(' || chars[i] == '{' || chars[i] == '[') {
        stack.add(chars[i]);
        } else {
        if (!stack.isEmpty()) {
        Character value = stack.pop();
        if (chars[i] == ')') {
        if (value != '(')
        return false;
        }
        if (chars[i] == '}') {
        if (value != '{')
        return false;
        }
        if (chars[i] == ']') {
        if (value != '[')
        return false;
        }
        } else {
        return false;
        }
        }
        }
        return stack.isEmpty();
    }
}