Add doubly linked list test (#100)

Author: lucic71

tests/unit/doubly_linked_list.cpp

@@ -0,0 +1,123 @@
+#include <cassert>
+
+struct Node {
+  int val;
+  Node *next;
+  Node *prev;
+
+  void SetNext(Node *n) { this->next = n; }
+  void SetPrev(Node *p) { this->prev = p; }
+};
+
+Node *Find(Node *head, int idx) {
+  Node *curr = head;
+  for (int i = 0; i < idx; i++) {
+    curr = curr->next;
+  }
+  return curr;
+}
+
+Node *FindBack(Node *tail, int idx) {
+  Node *curr = tail;
+  for (int i = 0; i < idx; i++) {
+    curr = curr->prev;
+  }
+  return curr;
+}
+
+void Append(Node &head, Node &new_node) {
+  Node *curr = &head;
+  while (curr->next != nullptr) {
+    curr = curr->next;
+  }
+  curr->SetNext(&new_node);
+  new_node.SetPrev(curr);
+}
+
+Node *Delete(Node *head, int val) {
+  Node *curr = head;
+  while (curr != nullptr) {
+    if (curr->val == val) {
+      Node *prev = curr->prev;
+      Node *next = curr->next;
+      if (prev != nullptr) {
+        prev->next = next;
+      }
+      if (next != nullptr) {
+        next->prev = prev;
+      }
+      if (prev != nullptr) {
+        return head;
+      } else {
+        return next;
+      }
+    }
+    curr = curr->next;
+  }
+  return head;
+}
+
+Node *Tail(Node *head) {
+  Node *curr = head;
+  while (curr->next != nullptr) {
+    curr = curr->next;
+  }
+  return curr;
+}
+
+int main() {
+  Node n0 = {5, nullptr, nullptr};
+  Node *head = &n0;
+  Node n1 = {4, nullptr, nullptr};
+  Node n2 = {3, nullptr, nullptr};
+  Node n3 = {2, nullptr, nullptr};
+  Node n4 = {1, nullptr, nullptr};
+  Node n5 = {0, nullptr, nullptr};
+  Node n6 = {-1, nullptr, nullptr};
+  Node n7 = {-2, nullptr, nullptr};
+  Append(*head, n1);
+  Append(*head, n2);
+  Append(*head, n3);
+  Append(*head, n4);
+  Append(*head, n5);
+  Append(*head, n6);
+  Append(*head, n7);
+  head = Delete(head, 5);
+  head = Delete(head, 0);
+  head = Delete(head, -2);
+  Node *tail = Tail(head);
+
+  assert(Find(head, 0)->val == 4);
+  assert(Find(head, 1)->val == 3);
+  assert(Find(head, 2)->val == 2);
+  assert(Find(head, 3)->val == 1);
+  assert(Find(head, 4)->val == -1);
+  assert(Find(head, 5) == nullptr);
+  assert(FindBack(tail, 0)->val == -1);
+  assert(FindBack(tail, 1)->val == 1);
+  assert(FindBack(tail, 2)->val == 2);
+  assert(FindBack(tail, 3)->val == 3);
+  assert(FindBack(tail, 4)->val == 4);
+  assert(FindBack(tail, 4)->prev == nullptr);
+
+  assert(Find(head, 0)->next->val == 3);
+  assert(Find(head, 1)->next->next->val == 1);
+  assert(Find(head, 2)->prev->val == 3);
+  assert(Find(head, 4)->next == nullptr);
+  assert(FindBack(tail, 1)->prev->prev->val == 3);
+
+  Find(head, 0)->next->val = 30;
+  assert(Find(head, 1)->val == 30);
+  Find(head, 1)->next->val = Find(head, 0)->val + Find(head, 3)->val;
+  assert(Find(head, 2)->val == 4 + 1);
+
+  int sum = Find(head, 0)->val + Find(head, 1)->val + Find(head, 2)->val +
+            Find(head, 3)->val + Find(head, 4)->val;
+  assert(sum == 4 + 30 + 5 + 1 + -1);
+
+  assert(Find(head, 0)->val + FindBack(tail, 0)->val == 4 + -1);
+  assert(Find(head, 2)->next->val == FindBack(tail, 1)->val);
+  assert(Find(head, 0)->prev == FindBack(tail, 4)->prev);
+
+  return 0;
+}