206. Clean solution

Author: MarshalX

main.cpp

@@ -10,15 +10,40 @@
 using namespace std;
 
 
+struct ListNode {
+    int val;
+    ListNode *next;
+    ListNode() : val(0), next(nullptr) {}
+    ListNode(int x) : val(x), next(nullptr) {}
+    ListNode(int x, ListNode *next) : val(x), next(next) {}
+};
+
 class Solution {
 public:
-  bool isPowerOfTwo(int n) {
-    if (n == -(1L << 31)) return false;
-    return __builtin_popcount(n) == 1;
+  ListNode* reverseList(ListNode* head) {
+    if (head == nullptr) {
+      return head;
+    }
+
+    ListNode* next = nullptr;
+    while (head != nullptr) {
+      auto tmp = head->next;
+      head->next = next;
+      next = head;
+      head = tmp;
+    }
+
+    return next;
   }
 };
 
 
 int main() {
+  auto r = Solution().reverseList(new ListNode(1, new ListNode(2, new ListNode(3, new ListNode(4)))));
+  while (r != nullptr) {
+    cout << r->val << " ";
+    r = r->next;
+  }
+
   return 0;
 }