Create n-ary-tree-preorder-traversal.py

Author: kamyu104

Python/n-ary-tree-preorder-traversal.py

@@ -0,0 +1,51 @@
+# Time:  O(n)
+# Space: O(h)
+
+# Given an n-ary tree, return the preorder traversal of its nodes' values.
+#
+# For example, given a 3-ary tree: 
+# Return its preorder traversal as: [1,3,5,6,2,4].
+#
+# Note: Recursive solution is trivial, could you do it iteratively?
+    
+# Definition for a Node.
+class Node(object):
+    def __init__(self, val, children):
+        self.val = val
+        self.children = children
+
+
+class Solution(object):
+    def preorder(self, root):
+        """
+        :type root: Node
+        :rtype: List[int]
+        """
+        if not root:
+            return []
+        result, stack = [], [root]
+        while stack:
+            node = stack.pop()
+            result.append(node.val)
+            for child in reversed(node.children):
+                if child:
+                    stack.append(child)
+        return result
+
+
+class Solution2(object):
+    def preorder(self, root):
+        """
+        :type root: Node
+        :rtype: List[int]
+        """
+        def dfs(root, result):
+            result.append(root.val)
+            for child in root.children:
+                if child:
+                    dfs(child, result)
+        
+        result = []
+        if root:
+            dfs(root, result)
+        return result