I used recursion to solve it. Base case is to check only root node and if it is null then reutn 0

else call left sub-tree recursively and keep adding 1 for each recursive level

do same for right subtree

Finally compare and return the larger value

...

public int maxDepth(TreeNode root) {

if(root==null) {

return 0;

}

int leftDepth = maxDepth(root.left)+1;

int rightDepth = maxDepth(root.right)+1;

```
if(leftDepth>=rightDepth) {
return leftDepth;
}
else {
return rightDepth;
}
}
```

...