[Leetcode] Intersection of two Linked Lists the intersection of two linked lists

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

For example, the following, linked lists:

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

Begin to intersect at node C1.

Notes:

• If The linked lists has no intersection at all, return null .
• The linked lists must retain their original structure after the function returns.
• You may assume there is 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.

I thought that in the future can not be free to do OJ, unexpectedly OJ and released the need to buy books can do the problem, the industry conscience ah, haha ^_^. If the humorous of the two linked list requires an O (n) execution time, it is not possible to use a similar bubbling method to find the same point, and it turns out that if the list is long, that method is inefficient. I also thought it would be like to delete the duplicate elements of the same as before the problem needs to use two pointers to traverse, but think for a long time did not think out how to do. Helpless Internet search the solution of the big God, found that the solution is very simple, because if the two chain length is the same, then the corresponding one to go down can be found, so only need to shorten the long list. The algorithm is as follows: Traverse two lists separately, get the corresponding length respectively. Then the length of the difference, the longer the linked list to move backward the number of differences, and then a comparison can be. The code is as follows:

/** Definition for singly-linked list. * struct ListNode {* int val; * ListNode *next; * ListNode (int x) : Val (x), Next (NULL) {}}; */classSolution { Public: ListNode*getintersectionnode (ListNode *heada, ListNode *headb) {        intLa =0, LB =0; ListNode*ha =Heada; ListNode*HB =headb;  while(Heada) {Heada= heada->Next; ++LA; }         while(headb) {headb= headb->Next; ++lb; }        intD = la-lb; if(D >0) {             for(inti =0; I < D; ++i) HA = ha->Next; } Else {             for(inti =0; I < D; ++i) HB = hb->Next; }         while(Ha && hB && ha! =HB) {HA= ha->Next; HB= hb->Next; }        if(HA && HB)returnHA; Else returnNULL; }};

[Leetcode] Intersection of two Linked Lists the intersection of two linked lists