Valid Parentheses

使用stack

简单一题做的复杂了

public class Solution {
    public boolean isValid(String s) {
        
	      Stack<Character> st = new Stack<Character>(); 
	      
	       int i = 0;
	       char bracket = '0';
	       boolean flag = true;
	       while( i<s.length() && flag == true){
	    	  if (s.charAt(i) == '(' || s.charAt(i) == '[' || s.charAt(i) == '{'){
	    		  st.push(s.charAt(i));
	    	  }
	    	  if (s.charAt(i) == ')' || s.charAt(i) == ']' || s.charAt(i) == '}' ){
	    	      if(!st.isEmpty()){
	    	         bracket = st.pop();
	    		     flag = matchMark(bracket,s.charAt(i));  
	    	      }
	    		  else{
	    	      flag=false;
	    	      }
	    	  }
	    	  
	    	  i++;
	       }
	       if (!flag) return false;
	       if (!st.empty()) return false;  //if parenthese, all elements pushed in should be pop out
	       else return true;
	      //return flag; 
    }
    private boolean matchMark(char c, char d) {
		
		// TODO Auto-generated method stub

 	   if(c == '(' && d == ')') return true;
 	   if(c == '{' && d == '}') return true;
 	   if(c == '[' && d == ']') return true;
 	   else return false;
    
	}
}