Intersection Point of Two Lists

Problem

Find where two singly linked lists merge.

a and b hold the node values, and a[skip_a:] and b[skip_b:] are the shared tail. Align the pointers by advancing the pointer in the longer tail by the length difference, then walk forward until the values first match.

Return the index in b where the shared tail begins, or -1 when there is no intersection.

Hint

Skip the length difference between the tails first so both pointers reach the shared part together.

Test cases

case 1

in: [[4,1,8,4,5],[5,6,1,8,4,5],2,3]

expected: 3

case 2

in: [[1,9,1,2,4],[3,2,4],3,1]

expected: 1

case 3

in: [[2,6,4],[1,5],3,2]

expected: -1

case 4

in: [[1],[1],0,0]

expected: 0

Starter codePython

def list_intersection(a, b, skip_a, skip_b):
    # Your code here
    pass

4 test cases · run your code against them in the editor