牛客刷题Java实现---二叉树的深度

输入一棵二叉树，求该树的深度。从根结点到叶结点依次经过的结点（含根、叶结点）形成树的一条路径，最长路径的长度为树的深度。

解题思路：利用层次遍历，遍历一层，层数加1.

class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }
}
public class Solution {
	public static void main(String[] args) {
		// 二叉树的深度
		// 输入一棵二叉树，求该树的深度。从根结点到叶结点依次经过的结点（含根、叶结点）形成树的一条路径，最长路径的长度为树的深度。
		TreeNode tn = new TreeNode(4);
		TreeNode tn1 = new TreeNode(5);
		TreeNode tn2 = new TreeNode(6);
		TreeNode tn3 = new TreeNode(7);
		TreeNode tn4 = new TreeNode(8);
		TreeNode tn5 = new TreeNode(9);
		TreeNode tn6 = new TreeNode(10);
		tn.left = tn1;
		tn.right = tn2;
		tn1.left=tn3;
		tn1.right=tn4;
		tn2.left=tn5;
		tn2.right=tn6;
		Solution s = new Solution();
		System.out.println(s.TreeDepth(tn));
	}

	public int TreeDepth(TreeNode root) {
		if(root==null){
			return 0;
		}
		int depth=0;
		TreeNode p=root;
		TreeNode last=root;
		Deque queue = new LinkedList();
		queue.addLast(p);
		while(queue.size()!=0){
			p=queue.peekFirst();
			queue.removeFirst();
			if(p.left != null){
				queue.addLast(p.left);
			}
			if(p.right != null){
				queue.addLast(p.right);
			}
			if(p==last){
				depth+=1;
				if(queue.size()!=0){
					last=queue.getLast();
				}
			}
		}
		return depth;
	}
}