[LintCode] 97 Maximum Depth of Binary Tree 解题报告

Description
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.


Example
Given a binary tree as follow:

      1
     / \
   2   3
  / \
4   5
The maximum depth is 3.

思路
当前子树的maxDepth就是左子树和右子树中最大的maxDepth加上1。

Code

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int maxDepth(TreeNode root) {
        // write your code here
        
        if (root == null) {
            return 0;
        }
        
        int leftMaxDepth = maxDepth(root.left);
        int rightMaxDepth = maxDepth(root.right);
        
        return Math.max(leftMaxDepth, rightMaxDepth) + 1;
    }
}