Poison

104. Maximum Depth of Binary Tree

发表于
DFS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
class Solution {
    private static class State {
        private int maxDepth;
    }

    public int maxDepth(TreeNode root) {
        State state = new State();
        dfs(root, 0, state);
        return state.maxDepth;
    }

    private void dfs(TreeNode root, int depth, State state) {
        if (root == null) {
            return;
        }

        state.maxDepth = Math.max(state.maxDepth, ++depth);
        dfs(root.left, depth, state);
        dfs(root.right, depth, state);
    }
}
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
26
27
class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }

        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);

        int depth = 0;

        while (!queue.isEmpty()) {
            depth++;
            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 depth;
    }
}
Reference

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