leetcode Valid Parentheses 有效括号

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.

exa:

"(){}[]"  true:

"{[()]}" true

"(}{}[]" false

按照括号规则必须首先出现‘（’或者‘{’，‘[’否则肯定不是合理括号组合，当‘（’或者‘{’，‘[’将对应的右括号')','}',']'入栈然后判断字符串下一个字符非‘（’或者‘{’，‘[’时是否等于刚刚入栈的字符即可：

class Solution {
private:
	stack<char>ss;
public:
    bool isValid(string s) {
		int l=s.length();
		if(l%2!=0||l==0)return false;
		int i;
		for(i=0;i<l;i++)
		{if(s[i]=='(')ss.push(')');
		else if(s[i]=='[')ss.push(']');
		else if(s[i]=='{')ss.push('}');
		else if((ss.empty()==true)||(ss.top()!=s[i])){return 0;}//先判断空，只有非空情况下再看ss.top，不能先看ss.top再判断空
		else ss.pop();}
		if(ss.empty())return 1;
		else return 0;
	}
};