160_intersection_of_two_linked_list.rb

# Leetcode Problem: https://leetcode.com/problems/intersection-of-two-linked-lists/
#Write a program to find the node at which the intersection of two singly linked lists begins.
#
# For example, the following two linked lists:
#
# begin to intersect at node c1.
#
#
#
# Example 1:
#
# Input: intersectVal = 8, listA = [4,1,8,4,5], listB = [5,6,1,8,4,5], skipA = 2, skipB = 3
# Output: Reference of the node with value = 8
# Input 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.
#
#
#
# Example 2:
#
# Input: intersectVal = 2, listA = [1,9,1,2,4], listB = [3,2,4], skipA = 3, skipB = 1
# Output: Reference of the node with value = 2
# Input 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: null
# Input 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.
#
#
#
# Notes:
#
#     If the two linked lists have no intersection at all, return null.
#     The linked lists must retain their original structure after the function returns.
#     You may assume there are no cycles anywhere in the entire linked structure.
#     Each value on each linked list is in the range [1, 10^9].
#     Your code should preferably run in O(n) time and use only O(1) memory.
# ----------------------------------------------------------------------------------------------------------------------
# Definition for singly-linked list.
# class ListNode
#     attr_accessor :val, :next
#     def initialize(val)
#         @val = val
#         @next = nil
#     end
# end

# @param {ListNode} headA
# @param {ListNode} headB
# @return {ListNode}
def getIntersectionNode(headA, headB)
  data = {}
  until headA.nil?
    data[headA] = true
    headA = headA.next
  end

  until headB.nil?
    return headB if data[headB]
    headB = headB.next
  end
end