forked from haoel/leetcode
-
Notifications
You must be signed in to change notification settings - Fork 0
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
New Problem Solution - "Linked List Random Node"
- Loading branch information
Showing
2 changed files
with
62 additions
and
0 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
61 changes: 61 additions & 0 deletions
61
algorithms/cpp/linkedListRandomNode/LinkedListRandomNode.cpp
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,61 @@ | ||
// Source : https://leetcode.com/problems/linked-list-random-node/ | ||
// Author : Hao Chen | ||
// Date : 2016-08-24 | ||
|
||
/*************************************************************************************** | ||
* | ||
* Given a singly linked list, return a random node's value from the linked list. Each | ||
* node must have the same probability of being chosen. | ||
* | ||
* Follow up: | ||
* What if the linked list is extremely large and its length is unknown to you? Could | ||
* you solve this efficiently without using extra space? | ||
* | ||
* Example: | ||
* | ||
* // Init a singly linked list [1,2,3]. | ||
* ListNode head = new ListNode(1); | ||
* head.next = new ListNode(2); | ||
* head.next.next = new ListNode(3); | ||
* Solution solution = new Solution(head); | ||
* | ||
* // getRandom() should return either 1, 2, or 3 randomly. Each element should have | ||
* equal probability of returning. | ||
* solution.getRandom(); | ||
***************************************************************************************/ | ||
|
||
/** | ||
* Definition for singly-linked list. | ||
* struct ListNode { | ||
* int val; | ||
* ListNode *next; | ||
* ListNode(int x) : val(x), next(NULL) {} | ||
* }; | ||
*/ | ||
class Solution { | ||
public: | ||
/** @param head The linked list's head. | ||
Note that the head is guaranteed to be not null, so it contains at least one node. */ | ||
Solution(ListNode* head) { | ||
this->head = head; | ||
this->len = 0; | ||
for(ListNode*p = head; p!=NULL; p=p->next, len++); | ||
srand(time(NULL)); | ||
} | ||
|
||
/** Returns a random node's value. */ | ||
int getRandom() { | ||
int pos = rand() % len; | ||
ListNode *p = head; | ||
for (; pos > 0; pos--, p=p->next); | ||
return p->val; | ||
} | ||
ListNode* head; | ||
int len; | ||
}; | ||
|
||
/** | ||
* Your Solution object will be instantiated and called as such: | ||
* Solution obj = new Solution(head); | ||
* int param_1 = obj.getRandom(); | ||
*/ |