30 minutes mock interview - written by the peer

using infix Expression to construct binary expression tree

convert infix expression to binary expression tree
for example, ((2 + 2)+3)

The solution written by the peer:

                   +
               +       3
            1     2    

    stack ( 
           + 
        +    3 
      1   2

     ((1+2)+3)
     
         +
       +    3
     1   2
     
     
class Solution {
    class Node {
        public String value;
        public Node left, right;
        public Node(String value) {
            this.value = value;
        }
    }   
    
    public Node convert(String s) {
        int n = s.length();
        if (n == 0) return null;
        Deque<Node> stack = new LinkedList<>();
        stack.addLast(new Node('+'));
        for(int i = 1; i < n; i++) {
           char ch = s.charAt(i);
           if (ch == '(' || Character.isDigit(ch)) {
               Node newNode = new Node(ch == '(' ? "+" : ch);
               Node node = stack.peekLast();
               if (node.left == null) node.left = newNode;
               else if (node.right == null) node.right = newNode;
                   stack.addLast(newNode);
               }               
           } 
        }
    }
}