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leetcode 160
160. 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.
找到两个单链表相交的点。此处假设单链表不存在环。
思路:首先获得两个单链表的长度,得到长度的差值n,然后将指向长链表的指针A先向后移动n位,之后指针A同指向短链表的指针B同时每次移动一位,当A与B指向同一节点时,该节点就是相交的结点。
1 /** 2 * Definition for singly-linked list. 3 * struct ListNode { 4 * int val; 5 * ListNode *next; 6 * ListNode(int x) : val(x), next(NULL) {} 7 * }; 8 */ 9 class Solution {10 public:11 ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {12 if(headA == NULL || headB == NULL)13 {14 return NULL;15 }16 ListNode * a = headA;17 ListNode * b = headB;18 int n = 1;19 int m = 1;20 while(headA->next != NULL)21 {22 headA = headA->next;23 n++;24 }25 while(headB->next != NULL)26 {27 headB = headB->next;28 m++;29 }30 if(headA != headB)31 {32 return NULL;33 }34 if(n > m)35 {36 for(int i = 0; i < n-m; i++)37 {38 a = a->next;39 }40 while(a)41 {42 if(a == b)43 {44 return a;45 }46 else47 {48 a = a->next;49 b = b->next;50 }51 }52 }53 else54 {55 for(int i = 0; i < m-n; i++)56 {57 b = b->next;58 }59 while(b)60 {61 if(a == b)62 {63 return a;64 }65 else66 {67 a = a->next;68 b = b->next;69 }70 }71 }72 return NULL;73 }74 };
拓展:
http://www.cppblog.com/humanchao/archive/2015/03/22/47357.html
leetcode 160
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