Leetcode45：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.

/** * 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) {      <span style="white-space:pre"></span>int lenA = 0;int lenB = 0;ListNode *head1 = headA;<span style="white-space:pre"></span>ListNode *head2 = headB;while (head1!=NULL){head1 = head1->next;lenA++;}while (head2!=NULL){head2 = head2->next;lenB++;}int n;if (lenA < lenB){n = lenB - lenA;head1 = headA;head2 = headB;for (int i = 0; i < n; i++){head2 = head2->next;}}else{n = lenA - lenB;head1 = headA;head2 = headB;for (int i = 0; i < n; i++){head1 = head1->next;}}while (head1 != head2){head1 = head1->next;head2 = head2->next;}return head1;    }};