leetcode@ [160]Intersection of Two Linked Lists
https://leetcode.com/problems/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: int getLength(ListNode *head){ int ret = 0; while(head != NULL){ head = head->next; ret++; } return ret; } ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) { int lenA = getLength(headA), lenB = getLength(headB); if(lenA > lenB){ int times = lenA -lenB; while(times--) headA = headA->next; } else{ int times = lenB- lenA; while(times--) headB = headB->next; } if(headA == headB && headA && headB) return headA; while(headA && headB){ headA = headA->next; headB = headB->next; if(headA == headB && headA && headB) return headA; } return NULL; } };