[LeetCode]104. Maximum Depth of Binary Tree

题目描述：

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.

思路：

求二叉树的最大深度。递归和迭代两种解法。
递归：如果根节点是null，则返回0
否则返回左子树或者右子树的深度+1

迭代：未做。

/*

public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) { val = x; }

*/

public class Solution104 {
    public int maxDepth(TreeNode root) {
        if(root == null) return 0;
        return Math.max(maxDepth(root.left),maxDepth(root.right))+1;
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Solution104 solution104 = new Solution104();
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(2);
        root.left.left = new TreeNode(3);
        root.left.right = new TreeNode(4);
        root.right.left = new TreeNode(4);
        //root.right.right = new TreeNode(3);
        root.right.left.left = new TreeNode(4);
        System.out.println(solution104.maxDepth(root));
    }

}