leetcode栈--5、valid-parentheses（有效括号）

题目描述

 

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：遇到任意一种左括号插入栈，遇到右括号，判断栈顶是否与其匹配，不匹配则无效，最后栈为空则有效

class Solution {
public:
    bool isValid(string s) {
       if(s.empty())
            return true;
        stack<char> ss;
        int n = s.size();
        for(int i=0;i<n;i++)
        {
            if(s[i] == '(' || s[i] =='[' || s[i] == '{')
            {
                ss.push(s[i]);
            }
            else
            {
                if(ss.empty())
                    return false;
                else
                {
                    if(ss.top() == '(' && s[i] == ')')
                    {
                        ss.pop();
                    }
                    else if(ss.top() == '[' && s[i] == ']')
                    {
                        ss.pop();
                    }
                    else if(ss.top() == '{' && s[i] == '}')
                    {
                        ss.pop();
                    }
                    else
                    {
                        return false;
                    }
                }
            }
        }
        if(ss.empty())
            return true;
        else
            return false; 
    }
};