vertical order traversal

Author: acharles7

trees/verticalOrderTraversal.py

@@ -0,0 +1,19 @@
+'''
+Given a binary tree, return the vertical order traversal of its nodes' values.
+(ie, from top to bottom, column by column).
+If two nodes are in the same row and column, the order should be from left to right.
+'''
+
+def verticalOrder(root):
+    if not root:return []
+    queue = [(root,0)]
+    hashmap = defaultdict(list)
+    while queue:
+        node, idx = queue.pop(0)
+        hashmap[idx] += [node.val]
+        if node.left:
+            queue.append((node.left, idx-1))
+        if node.right:
+            queue.append((node.right, idx+1))
+    output = [hashmap[i] for i in sorted(hashmap)]
+    return output