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116 lines
3.2 KiB
Markdown
116 lines
3.2 KiB
Markdown
# [160. Intersection of Two Linked Lists](https://leetcode.com/problems/intersection-of-two-linked-lists/)
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## 题目
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Write a program to find the node at which the intersection of two singly linked lists begins.
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For example, the following two linked lists:
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begin to intersect at node c1.
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**Example 1**:
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```
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Input: intersectVal = 8, listA = [4,1,8,4,5], listB = [5,0,1,8,4,5], skipA = 2, skipB = 3
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Output: Reference of the node with value = 8
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Input Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A, it reads as [4,1,8,4,5]. From the head of B, it reads as [5,0,1,8,4,5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B.
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```
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**Example 2**:
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```
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Input: intersectVal = 2, listA = [0,9,1,2,4], listB = [3,2,4], skipA = 3, skipB = 1
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Output: Reference of the node with value = 2
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Input Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A, it reads as [0,9,1,2,4]. From the head of B, it reads as [3,2,4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B.
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```
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**Example 3**:
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```
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Input: intersectVal = 0, listA = [2,6,4], listB = [1,5], skipA = 3, skipB = 2
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Output: null
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Input Explanation: From the head of A, it reads as [2,6,4]. From the head of B, it reads as [1,5]. Since the two lists do not intersect, intersectVal must be 0, while skipA and skipB can be arbitrary values.
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Explanation: The two lists do not intersect, so return null.
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```
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**Notes**:
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- If the two linked lists have no intersection at all, return null.
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- The linked lists must retain their original structure after the function returns.
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- You may assume there are no cycles anywhere in the entire linked structure.
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- Your code should preferably run in O(n) time and use only O(1) memory.
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## 题目大意
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找到 2 个链表的交叉点。
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## 解题思路
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这道题的思路其实类似链表找环。
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给定的 2 个链表的长度如果一样长，都从头往后扫即可。如果不一样长，需要先“拼成”一样长。把 B 拼接到 A 后面，把 A 拼接到 B 后面。这样 2 个链表的长度都是 A + B。再依次扫描比较 2 个链表的结点是否相同。
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## 代码
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```go
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package leetcode
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import "fmt"
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/**
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* Definition for singly-linked list.
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* type ListNode struct {
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* Val int
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* Next *ListNode
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* }
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*/
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func getIntersectionNode(headA, headB *ListNode) *ListNode {
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//boundary check
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if headA == nil || headB == nil {
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return nil
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}
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a := headA
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b := headB
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//if a & b have different len, then we will stop the loop after second iteration
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for a != b {
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//for the end of first iteration, we just reset the pointer to the head of another linkedlist
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if a == nil {
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a = headB
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} else {
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a = a.Next
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}
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if b == nil {
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b = headA
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} else {
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b = b.Next
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}
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fmt.Printf("a = %v b = %v\n", a, b)
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}
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return a
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}
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``` |