CareerCup

I'm going to assume that your tree is supposed to be the following because I can't read yours:

_________1
_______/___\
_____2______3
___/___\____/__\
__4____5__6___7
_/__\___/______/
8___9_10_____11
___/
__12

public static void printBottom(TreeNode node){
    Worker worker = new Worker(node);
    worker.execute();
    System.out.println(worker.getResults());
}

private static class Worker{
    TreeNode head;
    StringBuilder resultHolder;
    
    private Worker(TreeNode head){
        this.head = head;
    }

    private void execute(){
        this.resultHolder = new StringBuilder();
        this.executeRecur(this.head);
    }

    private void executeRecur(TreeNode node){
        if(node.left != null){
            printBottom(node.left);
        }
        if(node.left == null || node.right == null){
            this.resultHolder.append(node.value);
            this.resultHolder.append(' ');
        }
        if(node.right != null){
            printBottom(node.right);
        }
    }

    private String getResults(){
        if(this.resultHolder != null){
            return this.resultHolder.toString();
        }
        return null;
    }
}

It is a standard DFS traversal and print the leaf nodes that do not have any children.

It is a standard DFS traversal of the tree and print the nodes that do not have any child nodes.