104. Maximum Depth of Binary Tree

, ,

DFS

1
2
3
4
5
6
7
8
9
class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }

        return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
    }
}

BFS

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
class Solution {
    public int maxDepth(TreeNode root) {
        int maxDepth = 0;

        Queue<TreeNode> queue = new LinkedList<>();
        if (root != null) {
            queue.offer(root);
        }

        while (!queue.isEmpty()) {
            maxDepth++;
            for (int i = queue.size(); i > 0; i--) {
                TreeNode node = queue.poll();
                if (node.left != null) {
                    queue.offer(node.left);
                }
                if (node.right != null) {
                    queue.offer(node.right);
                }
            }
        }

        return maxDepth;
    }
}

References

104. Maximum Depth of Binary Tree
剑指 Offer 55 - I. 二叉树的深度