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 "([)]" are not.

 

public class Solution {
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<Character>();
        int len = s.length();
        
        for(int i = 0; i<len; i++){
            
            if(!stack.empty()){
                char top = stack.peek();
                char c = s.charAt(i);
              // 注意match 两个字符的顺序
                if(!match(top,c)){
                    stack.push(c);
                }else{
                    stack.pop();
                }
            }else{
                stack.push(s.charAt(i));
            }
        }
        
        if(!stack.empty()){
            return false;
        }else{
            return true;
        }
        
    }
    
    public boolean match(char a, char b){
        if(a == '(' && b ==')'){
            return true;
        } else if(a == '{' && b =='}'){
            return true;
        }else if(a == '[' && b ==']'){
            return true;
        }else{
            return false;
        }
    }
}