collections/linked-list: add LinkedList

src/collections/BUILD

@@ -3,3 +3,9 @@ cc_library(
     hdrs = ["vector.h"],
     visibility = ["//visibility:public"],
 )
+
+cc_library(
+    name = "linked-list",
+    hdrs = ["linked-list.h"],
+    visibility = ["//visibility:public"],
+)

src/collections/linked-list.h

@@ -0,0 +1,50 @@
+#ifndef _LINKED_LIST_
+#define _LINKED_LIST_
+
+#include <algorithm>
+
+template <typename T>
+class LinkedList {
+ public:
+  LinkedList() = default;
+  void push(T data) {
+    auto node = new Node(data);
+    if (this->tail == nullptr) {
+      this->tail = node;
+      this->head = this->tail;
+    } else {
+      this->tail->next = node;
+      this->tail = node;
+    }
+  }
+
+  T& operator[](size_t idx) {
+    auto walk = this->head;
+    if (walk == nullptr) {
+      throw "index out of range";
+    }
+
+    while (walk != nullptr && idx != 0) {
+      walk = walk->next;
+      idx--;
+    }
+
+    if (idx != 0) {
+      throw "index out of range";
+    }
+    return walk->data;
+  }
+
+ private:
+  struct Node {
+    T data;
+    Node* next = nullptr;
+    Node* prev = nullptr;
+    Node() = default;
+    Node(T data) : data(data) {}
+  };
+
+  Node* head = nullptr;
+  Node* tail = nullptr;
+};
+#endif /* ifndef _LINKED_LIST_ */

tests/BUILD

@@ -2,6 +2,7 @@ cc_test(
     name = "tests",
     srcs = glob(["*.cc"]),
     deps = [
+        "//src/collections:linked-list",
         "//src/collections:vector",
         "//src/math:number-theory",
         "@googletest//:gtest_main",

tests/test-linked-list.cc

@@ -0,0 +1,18 @@
+#include <gtest/gtest.h>
+
+#include <vector>
+
+#include "src/collections/linked-list.h"
+
+TEST(TestLinkedList, TestPush) {
+  LinkedList<int> list;
+  auto cases = std::vector<int>({1, 2, 3, 4, 5});
+
+  for (auto i : cases) {
+    list.push(i);
+  }
+
+  for (size_t i = 0; i < cases.size(); ++i) {
+    EXPECT_EQ(cases[i], list[i]);
+  }
+}

tests/test-number-theory.cc

@@ -1,9 +1,10 @@
-#include "src/math/number-theory.h"
-
 #include <gtest/gtest.h>
+
 #include <utility>
 #include <vector>
 
+#include "src/math/number-theory.h"
+
 TEST(TestGcd, TestCoprime) {
   std::vector<std::pair<int, int>> cases = {
       std::pair<int, int>(1, 7),   std::pair<int, int>(13, 7),

tests/test-vector.cc

@@ -1,4 +1,5 @@
 #include <gtest/gtest.h>
+
 #include "src/collections/vector.h"
 
 TEST(TestVec, TestSize) {