Intersection of Two Linked Lists两链表找重合节点

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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Linked List

/**
 * 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) {
        int lenA=0,lenB=0;
        ListNode *tempA=headA;
        ListNode *tempB=headB;
        while(tempA){
             lenA++;
             tempA=tempA->next;
        }
        while(tempB){
            lenB++;
            tempB=tempB->next;
        }
        while(lenA>lenB){
            headA=headA->next;
            lenA--;
        }
        while(lenB>lenA){
            headB=headB->next;
            lenB--;
        }
        while(headA != headB){
            headA=headA->next;
            headB=headB->next;
        }
        return headA;

    }
};