104. 二叉树的最大深度

递归解决

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
  int res = 0;

	public int maxDepth(TreeNode root) {
        if(root==null)
            return 0;
        depth(root,1);
		return res;
	}

	public void depth(TreeNode root, int i) {
		if (root.left != null) {
			depth(root.left,i+1);
		}
		if (root.right!= null) {
			depth(root.right,i+1);
		}
		this.res = Math.max(i, res);
	}
}

别的解法太精炼了

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int maxDepth(TreeNode root) {
        if(root==null)
            return 0;
        return 1+Math.max(maxDepth(root.left),maxDepth(root.right));
    }
}