leetcode Valid Parentheses

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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这个题我应该是见过的，但是具体在哪儿见过我不记得了。

刚开始想的比较简单，也打算用循环来做，发现这样很容易某个情况没有考虑到。陷入僵局。

后来猛然想起来——堆栈！

堆栈很适合这种匹配类问题啊，如果匹配了就出栈，如果没有匹配就压栈，等待匹配，最后看堆栈是否为空就行了。

 1 class Solution {
 2 public:
 3     bool isValid(string s) {
 4         int length=s.length(),i=1,temp=0;
 5         if(length%2!=0||length==0) return false;
 6         map<int,int> dic;
 7         dic[40]=41;
 8         dic[91]=93;
 9         dic[123]=125;
10         stack<char> match;
11         match.push(s[0]);
12         while(!match.empty()&&i<length){
13             temp=match.top();
14             if(dic.find(temp)==dic.end()) return false;
15             if(s[i]==dic[temp]){i++; match.pop();}
16             else match.push(s[i++]);
17         }
18         if(match.empty()) return true;
19         else return false;
20         
21     }
22 };