Create linked-list-random-node.cpp

Author: kamyu104

C++/linked-list-random-node.cpp

@@ -0,0 +1,32 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    /** @param head The linked list's head. Note that the head is guanranteed to be not null, so it contains at least one node. */
+    Solution(ListNode* head) : head_(head) {
+        
+    }
+    
+    /** Returns a random node's value. */
+    int getRandom() {
+        auto reservoir = head_->val;
+        auto n = 1;
+        for (auto curr = head_->next; curr; curr = curr->next) {
+            if (rand() % ++n == 0) {
+                reservoir = curr->val;
+            }
+        }
+        return reservoir;
+    }
+
+private:
+    ListNode *head_;
+};
+
+/**
+ * Your Solution object will be instantiated and called as such:
+ * Solution obj = new Solution(head);
+ * int param_1 = obj.getRandom();
+ */
+