Valid Parentheses

import java.util.HashMap;
import java.util.Map;
import java.util.Stack;


//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.
public class ValidParentheses {
 public boolean isValid(String s) {
 if(s==null||s.length()==0)
 return true;
      Map map=new HashMap();
  map.put('{', '}');
  map.put('[', ']');
  map.put('(', ')');
  Stack stack=new Stack();
  for(int i=0;i   char cur=s.charAt(i);
  if(map.keySet().contains(cur))
  stack.add(s.charAt(i));
  else if(map.values().contains(cur)){
  if(!stack.empty()&&cur==map.get(stack.peek())){
  stack.pop();
  }
  else {
return false;
}
  
  }
  }
  //注意stack空了才能是对的
  return stack.empty();
 
      
 }
}

Valid Parentheses