Merge in between linked lists

Author: volodimyr

1669.merge_in_between_linked_lists/merge.py

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+# 1669. Merge in between linked lists
+# Topics: 'Linked List'
+# Level: 'Medium'
+
+# You are given two linked lists: list1 and list2 of sizes n and m respectively.
+
+# Remove list1's nodes from the ath node to the bth node, and put list2 in their place.
+
+# The blue edges and nodes in the following figure indicate the result:
+
+# Build the result list and return its head.
+
+# Example 1:
+
+# Input: list1 = [10,1,13,6,9,5], a = 3, b = 4, list2 = [1000000,1000001,1000002]
+# Output: [10,1,13,1000000,1000001,1000002,5]
+# Explanation: We remove the nodes 3 and 4 and put the entire list2 in their place. The blue edges and nodes in the above figure indicate the result.
+
+# Example 2:
+
+# Input: list1 = [0,1,2,3,4,5,6], a = 2, b = 5, list2 = [1000000,1000001,1000002,1000003,1000004]
+# Output: [0,1,1000000,1000001,1000002,1000003,1000004,6]
+# Explanation: The blue edges and nodes in the above figure indicate the result.
+
+ 
+
+# Constraints:
+
+#     3 <= list1.length <= 104
+#     1 <= a <= b < list1.length - 1
+#     1 <= list2.length <= 104
+
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+class Solution:
+    def mergeInBetween(self, list1: ListNode, a: int, b: int, list2: ListNode) -> ListNode:
+        dummy = ListNode()
+        cur = list1
+        dcur = dummy
+        for i in range (a):
+            dcur.next = cur
+            dcur = dcur.next
+            cur = cur.next
+        curend = list1
+        for i in range (b):
+            curend = curend.next
+        dcur.next = list2
+        while dcur.next:
+            dcur = dcur.next
+        dcur.next = curend.next
+        return dummy.next

1669.merge_in_between_linked_lists/test_merge.py

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+from merge import ListNode
+from merge import Solution
+
+# Helper functions
+def create_linked_list(arr):
+    """Create a linked list from an array"""
+    if not arr:
+        return None
+    head = ListNode(arr[0])
+    current = head
+    for val in arr[1:]:
+        current.next = ListNode(val)
+        current = current.next
+    return head
+
+def linked_list_to_array(head):
+    """Convert a linked list to an array"""
+    result = []
+    current = head
+    while current:
+        result.append(current.val)
+        current = current.next
+    return result
+
+# Test cases
+def test_example_1():
+    """Example 1: Remove middle nodes and insert list2"""
+    sol = Solution()
+    list1 = create_linked_list([10, 1, 13, 6, 9, 5])
+    list2 = create_linked_list([1000000, 1000001, 1000002])
+    result = sol.mergeInBetween(list1, 3, 4, list2)
+    expected = [10, 1, 13, 1000000, 1000001, 1000002, 5]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 1 passed: Example 1")
+
+def test_example_2():
+    """Example 2: Remove larger range"""
+    sol = Solution()
+    list1 = create_linked_list([0, 1, 2, 3, 4, 5, 6])
+    list2 = create_linked_list([1000000, 1000001, 1000002, 1000003, 1000004])
+    result = sol.mergeInBetween(list1, 2, 5, list2)
+    expected = [0, 1, 1000000, 1000001, 1000002, 1000003, 1000004, 6]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 2 passed: Example 2")
+
+def test_remove_single_node():
+    """Remove a single node (a == b)"""
+    sol = Solution()
+    list1 = create_linked_list([1, 2, 3, 4, 5])
+    list2 = create_linked_list([10, 20])
+    result = sol.mergeInBetween(list1, 2, 2, list2)
+    expected = [1, 2, 10, 20, 4, 5]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 3 passed: Remove single node")
+
+def test_remove_at_start():
+    """Remove nodes starting from index 1"""
+    sol = Solution()
+    list1 = create_linked_list([1, 2, 3, 4, 5])
+    list2 = create_linked_list([100, 200])
+    result = sol.mergeInBetween(list1, 1, 2, list2)
+    expected = [1, 100, 200, 4, 5]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 4 passed: Remove at start")
+
+def test_remove_till_end():
+    """Remove nodes till near the end"""
+    sol = Solution()
+    list1 = create_linked_list([1, 2, 3, 4, 5, 6])
+    list2 = create_linked_list([100])
+    result = sol.mergeInBetween(list1, 2, 4, list2)
+    expected = [1, 2, 100, 6]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 5 passed: Remove till near end")
+
+def test_single_node_list2():
+    """list2 has only one node"""
+    sol = Solution()
+    list1 = create_linked_list([1, 2, 3, 4, 5])
+    list2 = create_linked_list([99])
+    result = sol.mergeInBetween(list1, 1, 3, list2)
+    expected = [1, 99, 5]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 6 passed: Single node list2")
+
+def test_long_list2():
+    """list2 is longer than the removed section"""
+    sol = Solution()
+    list1 = create_linked_list([1, 2, 3, 4])
+    list2 = create_linked_list([10, 20, 30, 40, 50])
+    result = sol.mergeInBetween(list1, 1, 1, list2)
+    expected = [1, 10, 20, 30, 40, 50, 3, 4]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 7 passed: Long list2")
+
+def test_minimum_list1():
+    """Minimum size list1 (3 nodes)"""
+    sol = Solution()
+    list1 = create_linked_list([1, 2, 3])
+    list2 = create_linked_list([100])
+    result = sol.mergeInBetween(list1, 1, 1, list2)
+    expected = [1, 100, 3]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 8 passed: Minimum list1")
+
+def test_large_values():
+    """Test with large values"""
+    sol = Solution()
+    list1 = create_linked_list([0, 1, 2, 3, 4])
+    list2 = create_linked_list([1000000, 9999999])
+    result = sol.mergeInBetween(list1, 2, 3, list2)
+    expected = [0, 1, 1000000, 9999999, 4]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 9 passed: Large values")
+
+def test_consecutive_range():
+    """Remove consecutive nodes in middle"""
+    sol = Solution()
+    list1 = create_linked_list([5, 10, 15, 20, 25, 30])
+    list2 = create_linked_list([100, 200, 300])
+    result = sol.mergeInBetween(list1, 2, 3, list2)
+    expected = [5, 10, 100, 200, 300, 25, 30]
+    assert linked_list_to_array(result) == expected, f"Expected {expected}, got {linked_list_to_array(result)}"
+    print("✓ Test 10 passed: Consecutive range")
+
+# Run all tests
+if __name__ == "__main__":
+    print("Running tests...\n")
+    test_example_1()
+    test_example_2()
+    test_remove_single_node()
+    test_remove_at_start()
+    test_remove_till_end()
+    test_single_node_list2()
+    test_long_list2()
+    test_minimum_list1()
+    test_large_values()
+    test_consecutive_range()
+    print("\n✅ All tests passed!")