Create vertical-order-traversal-of-a-binary-tree.py

Author: kamyu104

Python/vertical-order-traversal-of-a-binary-tree.py

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+# Time:  O(nlogn)
+# Space: O(n)
+
+# Definition for a binary tree node.
+class TreeNode(object):
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+
+class Solution(object):
+    def verticalTraversal(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[List[int]]
+        """
+        def dfs(node, lookup, x, y):
+            if not node:
+                return
+            lookup[x][y].append(node)
+            dfs(node.left, lookup, x-1, y+1)
+            dfs(node.right, lookup, x+1, y+1)
+                
+        lookup = collections.defaultdict(lambda: collections.defaultdict(list))
+        dfs(root, lookup, 0, 0)
+
+        result = []
+        for x in sorted(lookup):
+            report = []
+            for y in sorted(lookup[x]):
+                report.extend(sorted(node.val for node in lookup[x][y]))
+            result.append(report)
+        return result