Maximum Depth of Binary Tree

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本文介绍了两种计算二叉树最大深度的方法：一种是使用深度优先搜索递归地计算左右子树的最大深度；另一种是利用广度优先搜索逐层遍历二叉树，通过层级计数来确定最大深度。

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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.

求二叉树的最大深度，采用深度优先遍历原则

方法一：

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

方法二：广度优先遍历

public class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) {
			return 0;
		}
        LinkedList<TreeNode> currLevel =  new LinkedList<TreeNode>();
        currLevel.add(root);
        int count = 1;
        while (!currLevel.isEmpty()) {
	     	LinkedList<TreeNode> nextlevel = new LinkedList<TreeNode>();
	 		while (!currLevel.isEmpty()) {
	 			TreeNode node = currLevel.poll();
	 			if (node.left != null ) nextlevel.add(node.left);
	 			if (node.right != null) nextlevel.add(node.right);
	 		}
	 		if (!nextlevel.isEmpty()) {
	 			 count++;
	 			 currLevel = nextlevel;
			}
        }
        return count;
    }
}