代码实现

 
import org.example.TreeNode;
 
import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedList;
import java.util.List;
 
class Solution1 {
 
    int none = Integer.MIN_VALUE;
 
    public List> printTree(TreeNode root) {
 
        List> res = new ArrayList<>();
 
        Deque deque = new LinkedList<>();
        if (root != null) {
            deque.offer(root);
        }
 
        int countNotNull = deque.size();
        while (countNotNull != 0) {
            int sz = deque.size();
            List list = new ArrayList<>();
            countNotNull = 0;
            for (int i = 0; i < sz; i++) {
                TreeNode node = deque.poll();
                list.add((node.val));
                if (node.left != null) {
                    deque.offer(node.left);
                    countNotNull++;
                } else {
                    deque.offer(new TreeNode(none));
                }
                if (node.right != null) {
                    deque.offer(node.right);
                    countNotNull++;
                } else {
                    deque.offer(new TreeNode(none));
                }
            }
            res.add(list);
        }
 
 
        List> r = new ArrayList<>(res.size());
        int size = (int) Math.pow(2, res.size()) - 1;
 
        for (int i = 0; i < res.size(); i++) {
            List l = new ArrayList<>(size);
            r.add(l);
 
            List list = res.get(i);
 
            int v = (int) Math.pow(2, res.size()-i-1) - 1;
 
            for(int j=0;j
 
                // before
                for(int m=0;m
                    l.add("");
                }
                if(list.get(j) != none) {
                    l.add(String.valueOf(list.get(j)));
                } else {
                    l.add("");
                }
                // after
                for(int m=0;m
                    l.add("");
                }
 
                if(j != list.size()-1) {
                    l.add("");
                }
            }
 
        }
 
        return r;
    }
 
    public static void main(String[] args) {
        Solution1 solution = new Solution1();
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(3);
        root.left.right = new TreeNode(4);
        System.out.println(solution.printTree(root));
    }
}

总结

这道题就是二叉树的层序遍历+完全二叉树的特点的题目，感觉更像一个数学题目，先找到规律，然后用代码完成数据展示。欢迎有更高效、更简洁的思路回复。