LeetCode第20題之Valid Parentheses

方法一：用棧實現
C++代碼：

#include <stack>
#include <iostream>
using namespace std;
//Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

class Solution {
public:
    char reverse_char(char c)
    {
        switch(c)
        {
        case ')': return '(';
        case '}': return '{';
        case ']': return '[';
        default: return '\0';
        }
    }

    bool isValid(string s) {
        stack<char> sta;
        int sz = s.length();
        if (sz%2 != 0)
        {
            return false;
        }
        for (int i=0;i<sz;++i)
        {
            if ('(' == s[i] || '{' == s[i] || '[' == s[i])
            {
                sta.push(s[i]);
            }
            else if (')' == s[i] || '}' == s[i] || ']' == s[i])
            {
                if (0 == sta.size() || sta.top() != reverse_char(s[i]))
                {
                    return false;
                }
                sta.pop();
            }
        }
        if (0 == sta.size())
        {
            return true;
        }
        return false;
    }
};

int main()
{
    Solution s;
    cout<<s.isValid("{([])}");
    cout<<endl;
    cout<<s.isValid("{(])}");
    cout<<endl;
    return 0;
}