[leetcode]Valid Parentheses

Valid Parentheses

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Question Solution 

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.

很容易就想到使用堆栈来完成了。

不过本次堆栈有点复杂，使用了双向链表实现堆栈。

代码如下：

// test20ValidParentheses.cpp : 定义控制台应用程序的入口点。
//


#include "stdafx.h"
#include "string"


using std::string;
bool isValid(string s);
bool pushPar(char s);
char popPar();
bool stackIsNull();


struct ListNode {
char val;
ListNode *next;
ListNode *pre;
ListNode(int x) : val(x), next(NULL) {}


};
ListNode *head=NULL;
ListNode *cur = head;




int _tmain(int argc, _TCHAR* argv[])
{
bool res = isValid("head");
return 0;
}


bool isValid(string s) 
{
int n = s.size();
if (n < 1)
return true;
else
{
for (int i = 0; i < n; i++)
{
if (s[i] == '(' || s[i] == '[' || s[i] == '{')
{
pushPar(s[i]);
}

else if (s[i] == ')' || s[i] == ']' || s[i] == '}')
{
if (stackIsNull())
return false;
else
{
char ss = popPar();
if ((ss == '(' && s[i] != ')') || (ss == '[' && s[i] != ']') || (ss == '{' && s[i] != '}'))
return false;
}

}
}
if (stackIsNull())
return true;
else
return false;


}


}
bool pushPar(char s)
{
ListNode * temp;
temp = new ListNode(0);
temp->val = s;
temp->next = NULL;
if (head == NULL)
{
temp->pre = NULL;
head = temp;
cur = temp;
}
else
{
temp->pre = cur;
cur->next = temp;
cur = temp;
}
return true;
}
char popPar( )
{
char res = cur->val;
if (cur->pre == NULL)
{
cur = NULL;
head = NULL;
return res;
}
cur->pre->next = NULL;
cur = cur->pre;
return res;
}
bool stackIsNull()
{
if (head == NULL)
return true;
else
return false;
}