[leetcode] problem 160 – 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

No.1

Input: intersectVal = 8, listA = [4,1,8,4,5], listB = [5,0,1,8,4,5], 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 [5,0,1,8,4,5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B.

No.2

Input: intersectVal = 2, listA = [0,9,1,2,4], 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 [0,9,1,2,4]. 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.

No.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.

Note

Code

1
2
3
4
5

public class  {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14

public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
    if (headA == null || headB == null)
        return null;
    
    ListNode currentA = headA;
    ListNode currentB = headB;

    while (currentA != currentB) {
        currentA = currentA != null ? currentA.next : headB;
        currentB = currentB != null ? currentB.next : headA;
    }

    return currentA;
}