Leetcode 20. Valid Parentheses

一、题目要求：

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.

二、题目分析：

1.符合题意的形式还有：嵌套形式：{ [ ( ) ] } ,{ ( [] ) [ ] }

2.本题的经典在使用了栈的数据结构，先进后出，内层括号首先匹配，外层再进行匹配。

3.解题思路：

　　遍历所有输入的全部括号，

　　　　若是左括号，则压入栈中。

　　　　若是右括号，则和栈顶元素进行匹配。匹配成功则，则弹出栈顶元素，否则返回false,程序结束。

三、代码：

public class Solution {public boolean isValid(String s) {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 topChar=stack.peek();switch(c){case ')':if(topChar=='('){stack.pop();}else{return false;}break;case ']':if(topChar=='['){stack.pop();}else{return false;}break; case '}':if(topChar=='{'){stack.pop();}else{return false;}break;}}}if(stack.isEmpty()){return true;}else{return false;}}
}

转载于:https://www.cnblogs.com/lyr2015/p/6340361.html

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