Design Pattern 7: In-place Reversal of a LinkedList | Problem: Reverse every K-element Sub-list

7_reverse_nodes_in_k_group.cpp

@@ -0,0 +1,82 @@
+/* Problem: https://leetcode.com/problems/reverse-nodes-in-k-group/
+ */
+
+#include <iostream>
+#include <vector>
+
+//  Below ListNode definition is copied form problem
+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) {}
+};
+// Above ListNode definition is copied from problem
+
+std::ostream &operator<<(std::ostream &out, ListNode *node) {
+  out << "{";
+  while (node != nullptr) {
+    out << node->val << ", ";
+    node = node->next;
+  }
+  out << "}";
+  return out;
+  ;
+}
+
+ListNode *solution(ListNode *node, int k) {
+  if (k == 1)
+    return node;
+  ListNode *previous_group_last_node = nullptr, *current_node = node,
+           *head = node;
+  while (current_node != nullptr) {
+    ListNode *current_group_first_node = current_node;
+    int group_nodes_count;
+    for (group_nodes_count = 1; group_nodes_count < k; group_nodes_count++) {
+      if (current_node->next == nullptr) {
+        break;
+      }
+      current_node = current_node->next;
+    }
+    if (group_nodes_count == k) {
+      ListNode *current_group_last_node = current_node,
+               *next_group_first_node = current_node->next,
+               *left = current_group_first_node, *right = left->next;
+      if (head == node) {
+        head = current_group_last_node;
+      }
+      while (right != next_group_first_node) {
+        ListNode *tmp = right->next;
+        right->next = left;
+        left = right;
+        right = tmp;
+      }
+      if (previous_group_last_node != nullptr) {
+        previous_group_last_node->next = current_group_last_node;
+      }
+      previous_group_last_node = current_group_first_node;
+      current_group_first_node->next = next_group_first_node;
+      current_node = next_group_first_node;
+    } else {
+      break;
+    }
+  }
+  return head;
+}
+
+ListNode *vector_to_list(std::vector<int> &&vec) {
+  ListNode *head = nullptr;
+  for (int i = vec.size() - 1; i >= 0; i--) {
+    head = new ListNode(vec[i], head);
+  }
+  return head;
+}
+
+int main() {
+  std::cout << solution(vector_to_list({1, 2, 3, 4, 5}), 2) << std::endl
+            << solution(vector_to_list({1, 2, 3, 4, 5}), 3) << std::endl
+            << solution(vector_to_list({1, 2, 3, 4, 5}), 4) << std::endl;
+  ;
+  return 0;
+}

CMakeLists.txt

@@ -16,3 +16,5 @@ add_executable(3_squares_of_a_sorted_array 3_squares_of_a_sorted_array.cpp)
 add_executable(5_conflicting_appointments 5_conflicting_appointments.cpp)
 
 add_executable(6_find_all_missing_numbers 6_find_all_missing_numbers.cpp)
+
+add_executable(7_reverse_nodes_in_k_group 7_reverse_nodes_in_k_group.cpp)