题解 | #按之字形顺序打印二叉树#

import java.util.ArrayList; import java.util.LinkedList; import java.util.Queue; import java.util.Stack; /* public class TreeNode { int val = 0; TreeNode left = null; TreeNode right = null;

public TreeNode(int val) {
    this.val = val;

}

} */ //全网最差代码 public class Solution { public ArrayList<ArrayList > Print(TreeNode pRoot) { ArrayList<ArrayList> list = new ArrayList<>();

	Queue<TreeNode> queue = new LinkedList<>();
	Stack<TreeNode> stack = new Stack<>();
	queue.add(pRoot);
	
	ArrayList<Integer> list1;
	boolean flag = true;
	while(queue.peek() != null) {
		int qSize = queue.size();
		if(!flag) {
			list1 = new ArrayList<>();
			for(int i = 0;i < qSize;i++) {
				if(queue.peek().left != null) {
					queue.add(queue.peek().left);
				}
				if(queue.peek().right != null) {
					queue.add(queue.peek().right);
				}
                //由于要倒着来，因此可以放到栈里面
				stack.push(queue.peek());
				queue.poll();
			}
			while(!stack.empty()) {
				list1.add(stack.peek().val);//然后把栈里面的放到链表中
				stack.pop();
			}
			
			list.add(list1);
			flag = true;
		}else {//如果是奇数层
			list1 = new ArrayList<>();
			for(int i = 0;i < qSize;i++) {
				if(queue.peek().left != null) {
					queue.add(queue.peek().left);
				}
				if(queue.peek().right != null) {
					queue.add(queue.peek().right);
				}
				
                //直接就可以添加
				list1.add(queue.poll().val);
			}
			
			list.add(list1);
			flag = false;
		}
		
	}
	
	return list;
}

}