Leetcode-20. Valid Parentheses

前言：为了后续的实习面试，开始疯狂刷题，非常欢迎志同道合的朋友一起交流。因为时间比较紧张，目前的规划是先过一遍，写出能想到的最优算法，第二遍再考虑最优或者较优的方法。如有错误欢迎指正。博主首发CSDN，mcf171专栏。

博客链接：mcf171的博客

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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.

这个题没啥好说的，用一个堆实现即可。Your runtime beats 8.71% of java submissions.

public class Solution {
public boolean isValid(String s) {
Stack<Character> stack = new Stack<Character>();
Map<Character,Character> bracket2bracket = new HashMap<Character,Character>();
bracket2bracket.put(')','(');
bracket2bracket.put(']','[');
bracket2bracket.put('}','{');
for(int i = 0 ; i < s.length(); i++){
Character mapBracket = bracket2bracket.get(s.charAt(i));
if(mapBracket != null){
if(stack.empty()) return false;
char topChar = stack.pop();
if(topChar != mapBracket) return false;
}else{
stack.push(s.charAt(i));
}
}
if(stack.empty())	return true;
else return false;
}
}