Finding the Intersection Point of Two Linked Lists

You are given the heads of two singly linked lists, listA and listB. Your task is to find the node at which the two lists intersect. If the two lists do not intersect, you should return null. The intersection is defined based on reference, not value.

This problem is a classic in data structures and algorithms, testing your understanding of linked lists and your ability to devise efficient solutions. Identifying intersections is useful in various scenarios, such as detecting cycles in data structures or merging data streams.

Problem Description

Given two singly linked list heads, headA and headB, find the node where they intersect.

Key Requirements:

• The intersection is determined by the reference of the nodes. If node X is the intersection, then X must be present in both listA and listB. Subsequent nodes in listA and listB after the intersection point must also be identical.
• If no intersection exists, return null.
• You must not modify the original lists.

Expected Behavior:

• Return the intersecting node.
• If no intersection, return null.

Edge Cases to Consider:

• One or both lists are empty.
• The lists intersect at the very beginning (i.e., headA is the same node as headB).
• The lists intersect at the very end.
• The lists do not intersect at all.

Examples

Example 1:

listA = [4, 1, 8, 4, 5]
listB = [5, 6, 1, 8, 4, 5]
Intersection Node: Node with value 8

• Explanation:
  • listA starts with nodes 4 -> 1 -> 8 -> 4 -> 5.
  • listB starts with nodes 5 -> 6 -> 1 -> 8 -> 4 -> 5.
  • The node with value 8 is the first common node. After this node, the rest of the nodes (4 and 5) are also identical in both lists.

Example 2:

listA = [1, 9, 1, 2, 4]
listB = [3, 2, 4]
Intersection Node: Node with value 2

• Explanation:
  • listA starts with nodes 1 -> 9 -> 1 -> 2 -> 4.
  • listB starts with nodes 3 -> 2 -> 4.
  • The node with value 2 is the first common node. After this node, the node with value 4 is also identical in both lists.

Example 3:

listA = [2, 6, 4]
listB = [1, 5]
Intersection Node: null

• Explanation: The lists have no common nodes.

Constraints

• The number of nodes in each list is in the range [0, 3 * 10^4].
• The values of the nodes are not relevant for finding the intersection, only their references.
• You are guaranteed that if the two linked lists have no intersection at all, then neither list has a cycle.

Notes

• Think about how to handle lists of different lengths.
• Consider approaches that involve traversing the lists.
• An efficient solution would aim for a time complexity better than O(M*N), where M and N are the lengths of the lists.

Success is defined by correctly identifying and returning the intersection node, or null if no intersection exists, for all valid inputs adhering to the constraints.