Intersection of Two Linked Lists

Desicription

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

For example, the following two linked lists:

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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

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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
ListNode* pA = headA;
ListNode* pB = headB;
while(pA != pB) {
pA = pA?pA->next:headB;
pB = pB?pB->next:headA;
}
return pA;
}
};