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.
 
 
 class Solution {
 public:
     
     //解题思路：主要考虑()[]，([]),这两种 情况的讨论，可以重中间进行判断之后让其出栈再进行判断。
     
     bool isValid(string s) {
         stack<char>stack;
         for(int i=0;i<s.size();i++)
            {
             if(s[i]==')'||s[i]=='}'||s[i]==']')
                  {
                    if(stack.empty())
                        {
                        return false;
                    }
                    char c = stack.top();
                    if((c=='('&&s[i]==')')||(c=='{'&&s[i]=='}')||(c=='['&&s[i]==']'))
                     {
                     
                     stack.pop();
                 }
              }else{
                 stack.push(s[i]); 
              }
         }
            return stack.empty();        
     }
 };