New Problem Solution - "Linked List Random Node"

Author: haoel

README.md

@@ -14,6 +14,7 @@ LeetCode
 |385|[Mini Parser](https://leetcode.com/problems/mini-parser/) | [C++](./algorithms/cpp/miniParser/MiniParser.cpp)|Medium|
 |384|[Shuffle an Array](https://leetcode.com/problems/shuffle-an-array/) | [C++](./algorithms/cpp/shuffleAnArray/ShuffleAnArray.cpp)|Medium|
 |383|[Ransom Note](https://leetcode.com/problems/ransom-note/) | [C++](./algorithms/cpp/ransomNote/RansomNote.cpp)|Easy|
+|382|[Linked List Random Node](https://leetcode.com/problems/linked-list-random-node/) | [C++](./algorithms/cpp/linkedListRandomNode/LinkedListRandomNode.cpp)|Medium|
 |377|[Combination Sum IV](https://leetcode.com/problems/combination-sum-iv/) | [C++](./algorithms/cpp/combinationSumIV/combinationSumIV.cpp)|Medium|
 |376|[Wiggle Subsequence](https://leetcode.com/problems/wiggle-subsequence/) | [C++](./algorithms/cpp/wiggleSubsequence/wiggleSubsequence.cpp)|Medium|
 |350|[Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/) | [C++](./algorithms/cpp/intersectionOfTwoArraysII/intersectionOfTwoArraysII.cpp)|Easy|

algorithms/cpp/linkedListRandomNode/LinkedListRandomNode.cpp

@@ -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();
+ */