# 987. Vertical Order Traversal of a Binary Tree from collections import defaultdict """ given the 'root' of a binary tree, calcuate the vertical order traversal of the binary tree. for each node at position '(row, col)', its left and right children will be at positions '(row + 1, col - 1)' and '(row + 1, col + 1)' respectively. the root of the tree is at '(0, 0)'. the vertical order traversal of a binary tree is a list of top to bottom ordering for each column index starting from the leftmost column and ending on the rightmost column. there may be multiple nodes in the same row and same column. in such a case, sort these nodes by their values. return the vertical order traversal of the binary tree """ # Definition for a binary tree node. class TreeNode(object): def __init__(self, val=0, left=None, right=None): self.val = val self.left = left self.right = right class Solution(object): def helper(self, placement, level, root, _dict, limits): if not root: return _dict[placement].append((level, root.val)) limits[0] = min(limits[0], placement) limits[1] = max(limits[1], placement) self.helper(placement - 1, level + 1, root.left, _dict, limits) self.helper(placement + 1, level + 1, root.right, _dict, limits) def verticalTraversal(self, root): """ :type root: Optional[TreeNode] :rtype: List[List[int]] """ _dict = defaultdict(list) limits = [float("inf"), float("-inf")] self.helper(0, 0, root, _dict, limits) ans = [] for i in range(limits[0], limits[1] + 1): tmp = [] for j in sorted(_dict[i]): tmp.append(j[1]) ans.append(tmp) return ans if __name__ == "__main__": obj = Solution() print(obj.verticalTraversal(root=[3, 9, 20, None, None, 15, 7])) print(obj.verticalTraversal(root=[1, 2, 3, 4, 5, 6, 7])) print(obj.verticalTraversal(root=[1, 2, 3, 4, 6, 5, 7]))