[leetCode] 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.

public ListNode getIntersectionNode(ListNode headA, ListNode headB) {        if (headA == null || headB == null) return null;        int len1 = 0, len2 = 0;        ListNode tmpA = headA;        while(tmpA != null) {            len1++;            tmpA = tmpA.next;        }        tmpA = headA;        ListNode tmpB = headB;        while(tmpB != null) {            len2++;            tmpB = tmpB.next;        }        tmpB = headB;        if (len1 > len2) {            for (int i = 0; i < len1 - len2; i++) {                tmpA = tmpA.next;            }        }        else if (len1 < len2) {            for (int i = 0; i < len2 - len1; i++) {                tmpB = tmpB.next;            }        }        while(tmpA!= null) {            if (tmpA.equals(tmpB)) return tmpA;            tmpA = tmpA.next;            tmpB = tmpB.next;        }        return tmpA;    }