题解 | #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.*;
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> list=new ArrayList<>();
        dfs(pRoot,1,list);
        for (int i = 0; i < list.size(); i++) {
            if(i%2!=0){
                ArrayList<Integer> temp=list.get(i);
                Collections.reverse(temp);
                list.set(i,temp);
            }
        }
        return list;
    }
    public void dfs(TreeNode pRoot,int depth,ArrayList<ArrayList<Integer>> list){
        if(pRoot==null) return;
        if(depth>list.size()) list.add(new ArrayList<>());
        list.get(depth-1).add(pRoot.val);
        dfs(pRoot.left,depth+1,list);
        dfs(pRoot.right,depth+1,list);
    }
}