剑指Offer——按之字形顺序打印二叉树

import java.util.ArrayList;

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

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

    }

}
*/
import java.util.ArrayList;
import java.util.LinkedList;
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> listAll = new ArrayList<>();
        ArrayList<Integer> list = new ArrayList<>();
        if (pRoot == null) {
            return listAll;
        }
        LinkedList<TreeNode> queue = new LinkedList<>();
        int count = 1;
        int start = 0;
        //用于记录树中每一层的节点个数，当start==end的时候，表示当前层的节点已经全部添加进临时链表list中
        int end = 1;
        queue.add(pRoot);
        while (!queue.isEmpty()) {
            TreeNode temp = queue.pop();
            list.add(temp.val);
            start++;
            //这里必须是先把temp节点的左右子节点加进队列之后再去判断start是否和end相等，因为相等之后赋值的时候
            //需要把当前队列的长度赋值给end
            if (temp.left != null) {
                queue.add(temp.left);
            }
            if (temp.right != null) {
                queue.add(temp.right);
            }
            //当start==end的时候，表示当前层的节点已经全部添加进临时链表list中，需要把临时链表添加进listAll中
            //并且还要把end重新赋值为下一层的节点总个数值
            if (start == end) {
                if ((count & 1) == 0) {
                    end = queue.size();
                    start = 0;
                    ArrayList<Integer> list_temp = reverse(list);
                    listAll.add(list_temp);
                    list = new ArrayList<>();
                    
                } else {
                    end = queue.size();
                    start = 0;
                    listAll.add(list);
                    list = new ArrayList<>();
                }
                count++;
            }
        }
        return listAll;
    }
     private ArrayList<Integer> reverse(ArrayList<Integer> list) {
        if (list.size() == 0) {
            return null;
        }
        ArrayList<Integer> temp = new ArrayList<>();
        for (int i = list.size() - 1; i >= 0; i--) {
            temp.add(list.get(i));
        }
        return temp;
    }
}