[leetcode]--104. Maximum Depth of Binary Tree

Question 104：

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.

中文解释：求二叉树的最大深度

先给出结点的定义：

package leetcode.common;/** * 树的节点的定义,Use By 104 */public class TreeNode {    private int val;    private TreeNode left;    private TreeNode right;    public TreeNode(int x) { val = x; }    public int getVal() {        return val;    }    public void setVal(int val) {        this.val = val;    }    public TreeNode getLeft() {        return left;    }    public void setLeft(TreeNode left) {        this.left = left;    }    public TreeNode getRight() {        return right;    }    public void setRight(TreeNode right) {        this.right = right;    }}

解决思路：通过递归求二叉树的深度：
（1）root为空则返回零；
（2）root非空则返回 1 + （左子树深度 和 右子树深度 的最大值）；

package leetcode;import leetcode.common.TreeNode;import utils.LogUtil;public class Question104 {    /**     * 用递归做.     * @param root     * @return     */    public static int maxDepth(TreeNode root) {        if (root == null) return 0;        return 1 + Math.max(maxDepth(root.getLeft()), maxDepth(root.getRight())); //isLeaf is checked here    }    public static void main(String[] args) {        TreeNode root = new TreeNode(0);        root.setLeft(new TreeNode(1));        root.setRight(new TreeNode(2));        TreeNode left1 = root.getLeft();        left1.setLeft(new TreeNode(3));        LogUtil.log_debug("" + maxDepth(root));    }}

这个例子的运行结果：

2017-02-02 12:06:31：3