leetcode 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:

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.

Credits:
Special thanks to @stellari for adding this problem and creating all test cases.

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class Solution {public:ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {int lenA = 0, lenB = 0;ListNode *temp = headA;while(temp!=NULL) {lenA++;temp = temp->next;}temp = headB;while(temp!=NULL) {lenB++;temp = temp->next;}if(lenA<lenB) {temp = headA;headA = headB;headB = temp;}int diff = abs(lenB-lenA);for(int i = 0; i < diff; i++) {headA = headA->next;}for(;headA!=NULL && headA!=headB; headA=headA->next, headB=headB->next);return headA;}}