LeetCode20 Valid Parentheses的java 题解

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.
解题思路：
建立一个栈，输入如果是右括号直接压入栈，如果是左括号，若栈为空返回false，不为空就出栈，判断出栈的字符和输入的字符是否配对，处理完整个字符串后如果栈不为空返回false

代码：

public static boolean isValid(String s) {

Stack<Character> stack=new Stack<Character>();
Hashtable<Character, Character> hashtable=new Hashtable<>();
hashtable.put('(', ')');
hashtable.put('{', '}');
hashtable.put('[', ']');
char[] input=s.toCharArray();
for(int i=input.length-1;i>=0;i--)
{
if(input[i]==')'||input[i]=='}'||input[i]==']')
{
stack.push(input[i]);
}
else {
Character temp=null;
if(stack.empty())
return false;
else {
temp=stack.pop();
}
if(hashtable.get(input[i])!=temp)
return false;

}
}
if(stack.empty())
return true;
else {
return false;
}

}