# Intersection of Two Linked Lists

## Description

Write a program to find the node at which the intersection of two singly linked lists begins.

For example, the following two linked lists:

[![](https://assets.leetcode.com/uploads/2018/12/13/160_statement.png)](https://assets.leetcode.com/uploads/2018/12/13/160_statement.png)

begin to intersect at node c1.

**Example 1:**

[![](https://assets.leetcode.com/uploads/2018/12/13/160_example_1.png)](https://assets.leetcode.com/uploads/2018/12/13/160_example_1.png)

> **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.

**Example 2:**

[![](https://assets.leetcode.com/uploads/2018/12/13/160_example_2.png)](https://assets.leetcode.com/uploads/2018/12/13/160_example_2.png)

> **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.

**Example 3:**

[![](https://assets.leetcode.com/uploads/2018/12/13/160_example_3.png)](https://assets.leetcode.com/uploads/2018/12/13/160_example_3.png)

> **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.
* Your code should preferably run in O(n) time and use only O(1) memory.

## **Code**

```java
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        if (headA == null || headB == null) return null;
        
        ListNode tA = headA;
        ListNode tB = headB;
        
        while (tA != tB) {
            tA = tA == null ? headB : tA.next;
            tB = tB == null ? headA : tB.next;
        }
        return tA == null ? null : tA;
        
    }
}
```