Java---Judge whether a tree is a complete binary tree

Java—Determine whether a tree is a complete binary tree

Idea : Use breadth-first traversal for a complete binary tree, starting from the root node and entering the queue, if the queue is not empty, loop. When you encounter the first node without a left or right son, set the flag bit. If you encounter a node with a left or right son later, then this is not a complete binary tree. This method needs to traverse the entire tree, the complexity is O(N), and N is the total number of nodes.

code show as below:

/**
 * @Author shall潇
 * @Date 2021/3/4
 * @Description 
 */
 
public class CompleteTreeChecker {

	class Node {	//创建二叉树的数据结构
		int data;
		Node left;
		Node right;
}
	//实现广度遍历需要的队列
	private LinkedList<Node> queue = new LinkedList<Node>();
	//第n层最右节点的标志
	private boolean leftMost = false;
	
	public boolean processChild(Node child) {
		if(child != null) {
			if(!leftMost) {
				queue.addLast(child);
			} else {
				return false;
			}
		} else {
			leftMost = true;
		}
		return true;
	}
	
	public boolean isCompleteTree(Node root) {
		//空树也是完全二叉树
		if(root == null) return true;
		
		//首先根节点入队列
		queue.addLast(root);
		
		while(!queue.isEmpty()) {
			Node node = queue.removeFirst();
			
			//处理左子结点
			if(!processChild(node.left))
				return false;
			//处理右子结点
			if(!processChild(node.right))
				return false;
		}
		
		//广度优先遍历完毕，此树是完全二叉树
		return true;
	}
}