Intersection of Two Linked Lists

Intersection of Two Linked Lists is a Easy Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Linked List Manipulation Patterns pattern, in the Intersection Detection subpattern.

Problem statement

Given the heads of two singly linked-lists headA and headB, return the node at which the two lists intersect. If the two linked lists have no intersection at all, return null.

For example, the following two linked lists begin to intersect at node c1:

The test cases are generated such that there are no cycles anywhere in the entire linked structure.

Note that the linked lists must retain their original structure after the function returns.

Custom Judge:

The inputs to the judge are given as follows (your program is not given these inputs):

- intersectVal - The value of the node where the intersection occurs. This is 0 if there is no intersected node.

- listA - The first linked list.

- listB - The second linked list.

- skipA - The number of nodes to skip ahead in listA (starting from the head) to get to the intersected node.

- skipB - The number of nodes to skip ahead in listB (starting from the head) to get to the intersected node.

The judge will then create the linked structure based on these inputs and pass the two heads, headA and headB to your program. If you correctly return the intersected node, then your solution will be accepted.

Example 1:

Input: intersectVal = 8, listA = [4,1,8,4,5], listB = [5,6,1,8,4,5], skipA = 2, skipB = 3 Output: Intersected at '8' Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A, it reads as [4,1,8,4,5]. From the head of B, it reads as [5,6,1,8,4,5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B. - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words, they point to two different locations in memory, while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory.

Example 2:

Input: intersectVal = 2, listA = [1,9,1,2,4], listB = [3,2,4], skipA = 3, skipB = 1 Output: Intersected at '2' Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A, it reads as [1,9,1,2,4]. From the head of B, it reads as [3,2,4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B.

Example 3:

Input: intersectVal = 0, listA = [2,6,4], listB = [1,5], skipA = 3, skipB = 2 Output: No intersection Explanation: From the head of A, it reads as [2,6,4]. From the head of B, it reads as [1,5]. Since the two lists do not intersect, intersectVal must be 0, while skipA and skipB can be arbitrary values. Explanation: The two lists do not intersect, so return null.

Constraints:

- The number of nodes of listA is in the m.

- The number of nodes of listB is in the n.

- 1 <= m, n <= 3 104

- 1 <= Node.val <= 105

- 0 <= skipA <= m

Topics and companies

Topics: Hash Table, Linked List, Two Pointers.

Reported in interviews at Microsoft, Amazon, Facebook, Apple, ByteDance, Paypal, LinkedIn, Intuit.

How to practise Intersection of Two Linked Lists on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(1): All operations are direct index accesses and comparisons, no loops or recursion. time and O(1): No extra space is used beyond a few variables; input vectors are not copied or modified. space.

Open Intersection of Two Linked Lists in the code editor, or read the Intersection of Two Linked Lists editorial for a worked solution with its approach and complexity analysis.

Where Intersection of Two Linked Lists sits in the DSA pattern sheet

Problems related to Intersection of Two Linked Lists

Other problems that use the same Intersection Detection and Linked List Manipulation Patterns techniques:

Preparing this workspace.