Balanced Brackets (Valid Parentheses)

Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid.

An input string is valid if: Open brackets are closed by the same type of brackets and in the correct order.

Note that an empty string is also considered valid.

Example 1:
Input: "()"
Output: true
Example 2:
Input: "()[]{}"
Output: true
Example 3:
Input: "(]"
Output: false

Implementation

import java.util.HashMap;
import java.util.Map;
import java.util.Stack;
public class App {
    public static void main(String[] args) {
          String s = ")[]}";
          System.out.println(isValid(s));
    }
    public static boolean isValid(String s) {
              Stack<String> stack = new Stack<String>();
          Map<String,String> map = new HashMap<String,String>();
          map.put("]", "[");  map.put(")", "(");  map.put("}", "{");
          for(int i = 0; i < s.length(); i++) {
           String st = Character.toString(s.charAt(i));
           if(!map.containsKey(st)) {
             stack.push(st);
            } else {
            if(stack.isEmpty()) {
                            return false; 
              } else {
                            String peek = stack.peek();
                if(peek.equals(map.get(st))) {
                     stack.pop();
                 } else {
                    return false;
                 }
                          }
            }
         }
      return stack.isEmpty();
    }
}