Create 06. Extract Leaves of a Binary Tree in a Doubly Linked List.py

06_Binary-Trees/06. Extract Leaves of a Binary Tree in a Doubly Linked List.py

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+# https://practice.geeksforgeeks.org/problems/leaves-to-dll/1
+
+def convertToDLL(root):
+    #return the head of the DLL and remove those node from the tree as well.
+    notLeaves = set()
+
+    def isLeaves(root):
+        if not root.left and not root.right and root not in notLeaves: return True
+        return False
+
+    def addToDDL(node):
+        nonlocal cur
+        cur.right = node
+        node.left = cur
+        cur = cur.right
+
+    dummy = Node(-1)
+    cur = dummy
+
+    def dfs(root):
+        nonlocal cur
+        if not root: return
+        dfs(root.left)
+        if root.left and isLeaves(root.left):
+            node = root.left
+            root.left = None
+            addToDDL(node)
+            notLeaves.add(root)
+        if root.right and isLeaves(root.right):
+            node = root.right
+            root.right = None
+            addToDDL(node)
+            notLeaves.add(root)
+        dfs(root.right)
+
+    dfs(root)
+
+    res = dummy.right
+    dummy.right = None
+    res.left = None
+
+    return res
+
+