java 二叉树的最大深度

 二叉树的最大深度

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.

/**
 * 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;
         // 递归计算左子树深度
         l = maxDepth(root.left);
         // 递归计算右子树深度
         r = maxDepth(root.right);
        // 判断左右子树哪一个大则加一
        return l>r?l+1:r+1;
    }
}