Print a binary tree in an m*n 2D string array following these rules: 


The row number m should be equal to the height of the given binary tree.
The column number n should always be an odd number.
The root node's value (in string format) should be put in the exactly middle of the first row it can be put. The column and the row where the root node belongs will separate the rest space into two parts (left-bottom part and right-bottom part). You should print the left subtree in the left-bottom part and print the right subtree in the right-bottom part. The left-bottom part and the right-bottom part should have the same size. Even if one subtree is none while the other is not, you don't need to print anything for the none subtree but still need to leave the space as large as that for the other subtree. However, if two subtrees are none, then you don't need to leave space for both of them. 
Each unused space should contain an empty string "".
Print the subtrees following the same rules.


Example 1:

Input:
     1
    /
   2
Output:
[["", "1", ""],
 ["2", "", ""]]




Example 2:

Input:
     1
    / \
   2   3
    \
     4
Output:
[["", "", "", "1", "", "", ""],
 ["", "2", "", "", "", "3", ""],
 ["", "", "4", "", "", "", ""]]



Example 3:

Input:
      1
     / \
    2   5
   / 
  3 
 / 
4 
Output:

[["",  "",  "", "",  "", "", "", "1", "",  "",  "",  "",  "", "", ""]
 ["",  "",  "", "2", "", "", "", "",  "",  "",  "",  "5", "", "", ""]
 ["",  "3", "", "",  "", "", "", "",  "",  "",  "",  "",  "", "", ""]
 ["4", "",  "", "",  "", "", "", "",  "",  "",  "",  "",  "", "", ""]]



Note:
The height of binary tree is in the range of [1, 10].

Source: leetcode | Difficulty: MEDIUM_HARD
Tags: Tree algorithms

Graph traversal

Starter code: # Definition for a binary tree node.
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
    self.val = val
    self.left = left
    self.right = right
class Solution:
    def printTree(self, root: TreeNode) -> List[List[str]]:
        

Solutions:
class Solution:

	def printTree(self, root):

		def depth(root):
			if root is None:
				return 0
			return max(depth(root.left), depth(root.right)) + 1

		def printT(x, root, dep):
			if root is not None:
				ans[n - dep - 1][x] = str(root.val)
				printT(x - 2 ** (dep - 1), root.left, dep - 1)
				printT(x + 2 ** (dep - 1), root.right, dep - 1)
		n = depth(root)
		m = 2 ** n - 1
		ans = [[''] * m for __ in range(n)]
		printT((m - 1) // 2, root, n - 1)
		return ans


class Solution:

	def printTree(self, root):

		def depth(node):
			if node is None:
				return 0
			return 1 + max(depth(node.left), depth(node.right))
		d = depth(root)
		result = [[''] * (2 ** d - 1) for _ in range(d)]

		def helper(row, startcol, endcol, node):
			if node is None:
				return
			col = (startcol + endcol) // 2
			result[row][col] = str(node.val)
			helper(row + 1, startcol, col - 1, node.left)
			helper(row + 1, col + 1, endcol, node.right)
		helper(0, 0, 2 ** d - 2, root)
		return result


class Solution:

	def printTree(self, root):
		height = 0

		def Dfs(node, currHeight):
			nonlocal height
			if node == None:
				height = max(currHeight - 1, height)
				return
			Dfs(node.left, currHeight + 1)
			Dfs(node.right, currHeight + 1)
		Dfs(root, 1)
		ret = [[''] * (2 ** height - 1) for _ in range(height)]

		def rec(node, currHeight, start, end):
			if node == None:
				return
			center = int((start + end) / 2)
			ret[currHeight][center] = str(node.val)
			rec(node.left, currHeight + 1, start, center - 1)
			rec(node.right, currHeight + 1, center + 1, end)
		rec(root, 0, 0, 2 ** height - 1)
		return ret


class Solution:

	def printTree(self, root):
		if not root:
			return [[]]
		from queue import Queue
		(q, depth) = (Queue(), float('-inf'))
		q.put((root, 1))
		while not q.empty():
			(node, cur_depth) = q.get()
			depth = max(depth, cur_depth)
			if node.left:
				q.put((node.left, cur_depth + 1))
			if node.right:
				q.put((node.right, cur_depth + 1))
		col = 0
		for _ in range(depth):
			col = 2 * col + 1
		res = [[''] * col for _ in range(depth)]
		q.put((root, 0, 0, col - 1))
		while not q.empty():
			(node, depth, lo, hi) = q.get()
			mid = (lo + hi) // 2
			res[depth][mid] = str(node.val)
			if node.left:
				q.put((node.left, depth + 1, lo, mid - 1))
			if node.right:
				q.put((node.right, depth + 1, mid + 1, hi))
		return res


class Solution:

	def printTree(self, root):

		def depth(node):
			if not node:
				return 0
			return 1 + max(depth(node.left), depth(node.right))
		dep = depth(root)
		wid = 2 ** dep - 1
		frame = [['' for j in range(wid)] for i in range(dep)]

		def filler(node, level, low, high):
			if not node or low > high:
				return
			mid = (low + high) // 2
			frame[level][mid] = str(node.val)
			filler(node.left, level + 1, low, mid)
			filler(node.right, level + 1, mid + 1, high)
		filler(root, 0, 0, wid)
		return frame


class Solution:

	def printTree(self, root):

		def h(node):
			if not node:
				return 0
			return 1 + max(h(node.left), h(node.right))
		height = h(root)
		m = height
		n = 2 ** height - 1
		ret = [['' for _ in range(n)] for __ in range(m)]

		def put(node, i, l, r):
			mid = (l + r) // 2
			ret[i][mid] = str(node.val)
			if node.left:
				put(node.left, i + 1, l, mid - 1)
			if node.right:
				put(node.right, i + 1, mid + 1, r)
		put(root, 0, 0, n - 1)
		return ret


class Solution:

	def printTree(self, root):

		def getHeight(root):
			if not root:
				return 0
			return 1 + max(getHeight(root.left), getHeight(root.right))
		h = getHeight(root)
		w = 2 ** h - 1
		res = [[''] * w for _ in range(h)]

		def preorder(root, start, end, h):
			if not root:
				return
			mid = (start + end) // 2
			res[h][mid] = str(root.val)
			preorder(root.left, start, mid, h + 1)
			preorder(root.right, mid + 1, end, h + 1)
		preorder(root, 0, w, 0)
		return res


class Solution:

	def printTree(self, root):
		level = [root]
		tree = []
		while any(level):
			tree.append([str(node.val) if node else '' for node in level])
			level = [leaf for node in level for leaf in ((node.left, node.right) if node else (None, None))]
		ans = [['' for _ in range(2 ** len(tree) - 1)] for _ in range(len(tree))]
		for r in range(len(tree)):
			i = -2 ** (len(tree) - r - 1) - 1
			for c in tree[r]:
				i += 2 ** (len(tree) - r)
				ans[r][i] = c
		return ans


class Solution:

	def printTree(self, root):

		def depth(root):
			if root is None:
				return 0
			return 1 + max(depth(root.left), depth(root.right))

		def fill(res, root, i, l, r):
			if root is None:
				return
			res[i][(l + r) // 2] = str(root.val)
			fill(res, root.left, i + 1, l, (l + r) // 2)
			fill(res, root.right, i + 1, (l + r) // 2 + 1, r)
		height = depth(root)
		width = pow(2, height) - 1
		ans = []
		for i in range(height):
			ans.append([])
			for j in range(width):
				ans[i].append('')
		i = 0
		l = 0
		r = width
		fill(ans, root, 0, 0, width - 1)
		return ans


class Solution:

	def printTree(self, root):
		if not root:
			return ['']

		def getDepth(root):
			if not root:
				return 0
			return 1 + max(getDepth(root.left), getDepth(root.right))
		d = getDepth(root)
		cols = 2 ** d - 1
		result = [['' for i in range(cols)] for j in range(d)]

		def helper(root, d, pos):
			result[-d - 1][pos] = str(root.val)
			if root.left:
				helper(root.left, d - 1, pos - 2 ** (d - 1))
			if root.right:
				helper(root.right, d - 1, pos + 2 ** (d - 1))
		helper(root, d - 1, 2 ** (d - 1) - 1)
		return result