Finding max depth of binary tree without recursion

Question

Recursive mechanism to find max depth of depth of binary tree is very straightforward, but how can we do it efficiently without recursion as I have large tree where I would

Answer 1

Another way is to use Level order traversal, where tree height is equal to the number of level of a tree. (It can only be use to calulate the minimal height of a tree.)

public int maxDepth(TreeNode root) {
    if (root == null) return 0;
    LinkedList arr = new LinkedList(); // queue for current level
    LinkedList tmp = new LinkedList(); // queue for next level
    arr.add(root);
    int res = 0; // result
    TreeNode node; // tmp node 
    while (true) {
        while (!arr.isEmpty()) {
            node = arr.poll();
            if (node.left != null) tmp.add(node.left);
            if (node.right != null) tmp.add(node.right);
        }
        res++;
        if (tmp.isEmpty()) break;
        arr = tmp;
        tmp = new LinkedList();
    }
    return res;
}