Valid Parentheses 合法的匹配 栈实现

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 "([)]"

class Solution {
public:
    //栈实现
    bool isValid(string s) {
        int i;
        char pre;
        stack<char> ss;
        
        for(i=0;i<s.length();i++)
        {
            if(s[i]=='('||s[i]=='['||s[i]=='{')
                  ss.push(s[i]);
            else{//右边
                 if(ss.empty())    
                    return false;
                 pre=ss.top();//栈里面弹出左边的看是否匹配
                 switch(s[i]){
                    case ')':
                         if(pre=='(')
                             ss.pop();
                         else
                             return false;
                         break;
                    
                    case ']':
                        if(pre=='[')
                            ss.pop();
                         else
                            return false;
                         break;
                    case '}':
                        if(pre=='{')
                            ss.pop();
                        else
                            return false;
                        break;
                }
            }
        }
        if(ss.empty())
            return true;
        else
            return false;
    }
};