leetcode : valid parenttheses

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.

 

tag : stack, string

注意： hashmap。 map.keySet().contains(key). map.values().contains(value) 方法

public class Solution {
    public boolean isValid(String s) {
        
        if(s == null || s.length() == 0){
            return true;
        }
        
        if(s.length() % 2 != 0){
            return false;
        }
        
        HashMap<Character,Character> map = new HashMap<Character,Character>();
        map.put('(',')');
        map.put('[',']');
        map.put('{','}');
        Stack<Character> stack = new Stack<Character>();
        
        for(int i = 0; i < s.length(); i++){
            char cur = s.charAt(i);
            if(map.keySet().contains(cur)){
                stack.push(cur);
            }else if(map.values().contains(cur)){
                if(!stack.isEmpty() && map.get(stack.peek()) == cur){
                    stack.pop();
                }else{
                    return false;
                }
            }
        }
        
        return stack.isEmpty();
  
    }
}