160. Intersection of Two Linked Lists

#### QUESTION:

For example, the following two linked lists:

``````A:          a1 → a2
↘
c1 → c2 → c3
↗
B:     b1 → b2 → b3

``````

begin to intersect at node c1.

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.

#### SOLUTION:

``````public class Solution {
public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
HashSet<Integer> set = new HashSet<>();
while (headA!=null){
set.add(headA.val);
headA = headA.next;
}
while (headB!=null){
if(set.contains(headB.val))
return headB;
headB = headB.next;
}
return null;
}
}

public class Solution {
public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
if( null==headA || null==headB )
return null;

ListNode curA = headA, curB = headB;
while( curA!=curB){
curA = curA==null?headB:curA.next;
curB = curB==null?headA:curB.next;
}
return curA;
}
}
``````