LeetCode#20 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.

题意：给一串只包含有’(‘, ‘)’, ‘{‘, ‘}’, ‘[’ 和’]’,的字符串，要求判定是否是合法的。
思路：这个很自然就能想到用栈，典型的栈应用，复杂度O(n)。
代码：

class Solution {
public:
    bool isValid(string s) {
        stack<char>ch;
        int i,j;
        int len=s.size();
        for(i=0;iif(s[i]=='('||s[i]=='{'||s[i]=='[')
                ch.push(s[i]);    //入栈
            else 
            {
                if(ch.empty())return false;
                char temp=ch.top();
                if((s[i]==')'&&temp=='(')||(s[i]==']'&&temp=='[')||(s[i]=='}'&&temp=='{'))
                    ch.pop();    //出栈
                else return false;
            }
        }
        if(ch.empty())return true;
        else return false;
    }
};