6.9 完全二叉树的结点个数——【LeetCode】

package com.tree.java;

import java.util.linkedList;

public class seven {
	//递归法：
	public int countNodes(TreeNode root) {
		if(root == null) {
			return 0;
		}
		return countNodes(root.left) + countNodes(root.right) + 1;
	}
	
	//迭代法：
	public int countNodes1(TreeNode root) {
		if(root == null) {
			return 0;
		}
		linkedList queue = new linkedList<>();
		queue.offer(root);	
		int result = 0;
		while(!queue.isEmpty()) {
			int size = queue.size();
			while(size > 0) {
				TreeNode cur = queue.poll();
				result++;
				
				if(cur.left != null) {
					queue.offer(cur.left);
				}
				if(cur.right != null) {
					queue.offer(cur.right);
				}
				
				size--;
			}
		}
		return result;
	}
}

class TreeNode {
	
	int val;
	TreeNode left;
	TreeNode right;
	TreeNode() {}
	TreeNode(int val) { this.val = val; }
	TreeNode(int val, TreeNode left, TreeNode right) {
		this.val = val;
	    this.left = left;
	    this.right = right;
	}
}