题解 | #按之字形顺序打印二叉树#

import java.util.*;

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

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

    }

}
*/
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer> > res = new ArrayList<ArrayList<Integer> >();
        ArrayList<Integer> list = new ArrayList<Integer>();
        // pRoot为空
        if(pRoot == null){
            return res;
        }
        // pRoot不为空
        ArrayList<TreeNode> nodes = new ArrayList<TreeNode>();
        TreeNode temp = null;
        int size = 0;
        int index = 0;
        nodes.add(pRoot);
        while(nodes.size() != 0){
            size = nodes.size();
            index++;
            for(int i = 0;i < size;i++){
                temp = nodes.remove(0);
                if(temp.left != null){
                    nodes.add(temp.left);
                }
                if(temp.right != null){
                    nodes.add(temp.right);
                }
                list.add(temp.val);
            }
            if(index % 2 == 1){
                res.add(new ArrayList<Integer>(list));
            } else{
                Collections.reverse(list);
                res.add(new ArrayList<Integer>(list));
            }
            list.clear();
        }
        return res;
    }
}