Maximum Depth of Binary Tree

LC104

time complexity: o(n)， 空间是栈高度O(logn)

public class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null ) return 0;
        int left = maxDepth(root.left);
        int right = maxDepth(root.right);

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