Leetcode_104_Maximum Depth of Binary Tree

[lihe]

Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its depth = 3.

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

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