Count Complete Tree Nodes(Medium)

Given a complete binary tree, count the number of nodes.

Definition of a complete binary tree from Wikipedia: In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.

public int countNodes(TreeNode root) {  
        if(root==null) return 0;  

        int l = getLeft(root) + 1;  
        int r = getRight(root) + 1;  

        if(l==r) {  
            return (2<<(l-1)) - 1;  
        } else {  
            return countNodes(root.left) + countNodes(root.right) + 1;  
        }  
    }  

    private int getLeft(TreeNode root) {  
        int count = 0;  
        while(root.left!=null) {  
            root = root.left;  
            ++count;  
        }  
        return count;  
    }  

    private int getRight(TreeNode root) {  
        int count = 0;  
        while(root.right!=null) {  
            root = root.right;  
            ++count;  
        }  
        return count;  
    }