剑指 Offer 32 - III. 从上到下打印二叉树 III

package leetcode;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.Stack;

public class offer_32_3 {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> list=new ArrayList<List<Integer>>();
        //使用链表
        LinkedList<TreeNode> queue=new LinkedList<TreeNode>();
        if(root==null) {return list;}
        int begin=0;
        int oldend;
        int end=0;
        int level=0;
        queue.addFirst(root);
        while(!queue.isEmpty()) {
            oldend=end;
            List<Integer> l=new ArrayList<Integer>();
            TreeNode temp;
            //偶数行从链表头读取，并将子节点按左右存入
            if(level%2==0) {
                while(begin<=oldend) {
                    temp=queue.removeFirst();
                    l.add(temp.val);
                    if(temp.left!=null) {
                        queue.addLast(temp.left);
                        end=end+1;
                    }
                    if(temp.right!=null) {
                        queue.addLast(temp.right);
                        end=end+1;
                    }
                    begin=begin+1;
                }
            }else {
                //奇数行从链表尾读取，并将子节点按右左存入
                while(begin<=oldend) {
                    temp=queue.removeLast(); 
                    l.add(temp.val);
                    if(temp.right!=null) {
                        queue.addFirst(temp.right);
                        end=end+1;
                    }
                    if(temp.left!=null) {
                        queue.addFirst(temp.left);
                        end=end+1;
                    }
                    begin=begin+1;
                }
            }
            list.add(l);
            //记录行数
            level=level+1;
        }
        return list;
    }
}