PattySung

Given the root of a binary tree, return its maximum depth.

A binary tree’s maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. ->給定一個二元樹並找到它的最大深度，最大深度是指從最上層節點至最下層節點之間所經過的節點數。

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: 3

Example 2:

Input: root = [1,null,2]
Output: 2

<解題>

找左子樹的深度和右子樹的深度較大的


class Solution {
    public int maxDepth(TreeNode root) {
        if(root==null){
            return 0;
        }
        return 1+Math.max(maxDepth(root.left),maxDepth(root.right));
    }
}

Time complexity: O(n) Space complexity: O(n)


class Solution {
    public int maxDepth(TreeNode root) {
    if(root == null) {
        return 0;
    }
    Queue<TreeNode> queue = new LinkedList<>();
    queue.offer(root);
    int count = 0;
    while(!queue.isEmpty()) {
        int size = queue.size();
        while(size-- > 0) {
            TreeNode node = queue.poll();
            if(node.left != null) {
                queue.offer(node.left);
            }
            if(node.right != null) {
                queue.offer(node.right);
            }
        }
        count++;
    }
    return count;
}
}

Leetcode-104. Maximum Depth of Binary Tree

<解題>