diff --git a/.gitignore b/.gitignore
index 1d2aac8..a0bd8de 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,7 @@
 /bazel-*
 .vscode
 .idea
+.ccls-cache
+.clwb
+vgcore.*
+.gdb_history
diff --git a/src/collections/BUILD b/src/collections/BUILD
index 5e61254..83d282b 100644
--- a/src/collections/BUILD
+++ b/src/collections/BUILD
@@ -3,3 +3,9 @@ cc_library(
     hdrs = ["vector.h"],
     visibility = ["//visibility:public"],
 )
+
+cc_library(
+    name = "skiplist",
+    hdrs = ["skiplist.h"],
+    visibility = ["//visibility:public"],
+)
diff --git a/src/collections/skiplist.h b/src/collections/skiplist.h
new file mode 100644
index 0000000..4684cc7
--- /dev/null
+++ b/src/collections/skiplist.h
@@ -0,0 +1,260 @@
+#ifndef SKIP_LIST
+#define SKIP_LIST
+
+#include <algorithm>
+#include <cstdlib>
+#include <cstring>
+#include <functional>
+#include <iostream>
+#include <iterator>
+
+#define LEVEL_RATE 0.5
+
+template <typename K, typename V, typename Comparator = std::less<K> >
+class SkipList {
+ private:
+  struct Node {
+    K key;
+    V value;
+    size_t level_num{};
+    struct nodeLevel {
+      struct Node *forward;
+    } * level;
+    Node(K key, V value, int level) {
+      this->key = key;
+      this->value = value;
+      this->level = new nodeLevel[level];
+      this->level_num = level;
+      std::memset(this->level, 0, sizeof(struct nodeLevel *) * level);
+    }
+
+    Node(const Node &other) {
+      this->key = other.key;
+      this->value = other.value;
+      this->level_num = other.level_num;
+      std::copy(other.level, other.level + level_num, this->level);
+    }
+
+    virtual ~Node() { delete[] this->level; }
+  };
+
+  static const size_t MAXLEVEL = 32;
+  int largestLevel{};
+  Node *header, *tail;
+  size_t len;
+  Comparator cmp;
+
+  static int randomLevel();
+
+ public:
+  SkipList(Comparator comparator);
+  SkipList(const SkipList<K, V, Comparator> &other);
+  SkipList &operator=(const SkipList<K, V, Comparator> &other);
+  virtual ~SkipList();
+
+  Node *insert(K key, V value, bool replace = false);
+  Node *search(const K &key);
+  bool remove(const K &key);
+  size_t size() const;
+
+  class iterator;
+  iterator begin() const;
+  iterator end() const;
+};
+
+template <typename K, typename V, typename Comparator>
+SkipList<K, V, Comparator>::SkipList(Comparator comparator) : cmp(comparator) {
+  this->len = 0;
+  this->header = new Node(K(), V(), MAXLEVEL);
+
+  for (size_t i = 0; i < MAXLEVEL; i++) {
+    this->header->level[i].forward = nullptr;
+  }
+
+  this->largestLevel = 1;
+  this->tail = nullptr;
+}
+
+template <typename K, typename V, typename Comparator>
+SkipList<K, V, Comparator>::~SkipList() {
+  Node *node = this->header->level[0].forward, *next;
+  delete this->header;
+  while (node) {
+    next = node->level[0].forward;
+    delete node;
+    node = next;
+  }
+}
+
+// http://www.voidcn.com/article/p-mwawflgq-bgg.html
+template <typename K, typename V, typename Comparator>
+int SkipList<K, V, Comparator>::randomLevel() {
+  int level = 1;
+
+  while ((random() & 0xFFFF) < (LEVEL_RATE * 0xFFFF)) level += 1;
+
+  return (level < signed(MAXLEVEL)) ? level : MAXLEVEL;
+}
+
+template <typename K, typename V, typename Comparator>
+SkipList<K, V, Comparator>::SkipList(const SkipList<K, V, Comparator> &other) {
+  SkipList nl = SkipList(other.cmp);
+  nl.largestLevel = other.largestLevel;
+  nl.len = other.len;
+  Node *head = other.header, *next;
+  for (size_t i = 0; i < nl.len; i++) {
+    next = head->level[0].forward;
+    *head = Node(*head);
+    head = next;
+  }
+}
+
+template <typename K, typename V, typename Comparator>
+typename SkipList<K, V, Comparator>::Node *SkipList<K, V, Comparator>::insert(
+    K key, V value, bool replace) {
+  // store the level and the position to insert After
+  Node *update[MAXLEVEL], *x;
+  Comparator lessThan = this->cmp;
+  bool replacedTag = false;
+
+  Node *r = nullptr;
+  x = this->header;
+  for (int i = this->largestLevel - 1; i >= 0; i--) {
+    while (x->level[i].forward && /*this level enable*/
+           lessThan(x->level[i].forward->key, key)) {
+      x = x->level[i].forward;
+    }
+
+    // equal key conflict
+    if (x->level[i].forward && !lessThan(x->level[i].forward->key, key) &&
+        !lessThan(key, x->level[i].forward->key)) {
+      if (!replace)
+        return nullptr;
+      else {
+        x->level[i].forward->value = value;
+        replacedTag = true;
+        if (r == nullptr) r = x->level[i].forward;
+      }
+    }
+    update[i] = x;
+  }
+
+  // replaced no need to update and create new node
+  if (replacedTag) return r;
+
+  int level_num = randomLevel();
+  if (level_num > this->largestLevel) {
+    for (int i = this->largestLevel; i < level_num; i++) {
+      update[i] = this->header;
+    }
+    this->largestLevel = level_num;
+  }
+  x = new Node(key, value, level_num);
+
+  for (int i = 0; i < level_num; i++) {
+    x->level[i].forward = update[i]->level[i].forward;
+    update[i]->level[i].forward = x;
+  }
+
+  this->len++;
+  if (x->level[0].forward == nullptr) this->tail = x;
+  return x;
+}
+
+template <typename K, typename V, typename Comparator>
+inline size_t SkipList<K, V, Comparator>::size() const {
+  return this->len;
+}
+
+template <typename K, typename V, typename Comparator>
+typename SkipList<K, V, Comparator>::Node *SkipList<K, V, Comparator>::search(
+    const K &key) {
+  Node *x = this->header, *ret = nullptr;
+  Comparator less = this->cmp;
+  for (int i = this->largestLevel - 1; i >= 0; i--) {
+    while (x->level[i].forward && less(x->level[i].forward->key, key)) {
+      x = x->level[i].forward;
+    }
+
+    // equal just return
+    if (x->level[i].forward && !less(x->level[i].forward->key, key) &&
+        !less(key, x->level[i].forward->key)) {
+      ret = x->level[i].forward;
+      return ret;
+    }
+  }
+  return ret;
+}
+
+template <typename K, typename V, typename Comparator>
+bool SkipList<K, V, Comparator>::remove(const K &key) {
+  Node *x = this->header, *update[MAXLEVEL];
+  ;
+  bool ret = false;
+  Comparator less = this->cmp;
+  for (int i = this->largestLevel - 1; i >= 0; i--) {
+    while (x->level[i].forward && less(x->level[i].forward->key, key)) {
+      x = x->level[i].forward;
+    }
+    update[i] = x;
+  }
+
+  if (x->level[0].forward && !less(x->level[0].forward->key, key) &&
+      !less(key, x->level[0].forward->key)) {
+    Node *del = x->level[0].forward;
+    for (int j = 0; j < this->largestLevel; j++) {
+      if (update[j]->level[j].forward == del) {
+        update[j]->level[j].forward = del->level[j].forward;
+      }
+    }
+
+    ret = true;
+    if (del->level[0].forward == nullptr) this->tail = del;
+    while (this->largestLevel > 1 &&
+           this->header->level[this->largestLevel - 1].forward == nullptr)
+      this->largestLevel--;
+    this->len--;
+  }  // find one
+
+  return ret;
+}
+
+// Iterator
+template <typename K, typename V, typename Comparator>
+class SkipList<K, V, Comparator>::iterator
+    : std::iterator<std::forward_iterator_tag,
+                    typename SkipList<K, V, Comparator>::Node> {
+ private:
+  Node *curr;
+
+ public:
+  iterator(Node *n) : curr(n){};
+  iterator(const iterator &other) { this->curr = other.curr; }
+  iterator &operator++() {
+    this->curr = this->curr->level[0].forward;
+    return *this;
+  }
+  iterator &operator++(int) {
+    auto tmp = this;
+    this->curr = this->curr->level[0].forward;
+    return *tmp;
+  }
+  bool operator==(const iterator &rhs) { return rhs.curr == this->curr; }
+  bool operator!=(const iterator &rhs) { return !(rhs.curr == this->curr); }
+  Node *operator->() { return curr; }
+  Node &operator*() { return *curr; }
+};
+
+template <typename K, typename V, typename Comparator>
+typename SkipList<K, V, Comparator>::iterator
+SkipList<K, V, Comparator>::begin() const {
+  return SkipList::iterator(this->header->level[0].forward);
+}
+
+template <typename K, typename V, typename Comparator>
+typename SkipList<K, V, Comparator>::iterator SkipList<K, V, Comparator>::end()
+    const {
+  return SkipList::iterator(nullptr);
+}
+
+#endif  // SKIP_LIST
diff --git a/tests/BUILD b/tests/BUILD
index ccd1218..12bb882 100644
--- a/tests/BUILD
+++ b/tests/BUILD
@@ -2,6 +2,7 @@ cc_test(
     name = "tests",
     srcs = glob(["*.cc"]),
     deps = [
+        "//src/collections:skiplist",
         "//src/collections:vector",
         "//src/math:number-theory",
         "@googletest//:gtest_main",
diff --git a/tests/test-number-theory.cc b/tests/test-number-theory.cc
index 90a6bf8..2489fd4 100644
--- a/tests/test-number-theory.cc
+++ b/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),
diff --git a/tests/test-skiplist.cc b/tests/test-skiplist.cc
new file mode 100644
index 0000000..b00a348
--- /dev/null
+++ b/tests/test-skiplist.cc
@@ -0,0 +1,62 @@
+#include <gtest/gtest.h>
+
+#include <iostream>
+#include <string>
+#include <vector>
+
+#include "src/collections/skiplist.h"
+
+TEST(SkipList, Constrcutor) {
+  auto lst = SkipList<std::string, std::string>(std::less<std::string>());
+  EXPECT_EQ(lst.size(), 0);
+}
+
+TEST(SkipList, Insert) {
+  auto lst = SkipList<std::string, std::string>(std::less<std::string>());
+  lst.insert("key", "value");
+  EXPECT_EQ(lst.size(), 1);
+  auto np = lst.search("key");
+  EXPECT_EQ(np->value, "value");
+  lst.insert("abc", "ABC");
+  EXPECT_EQ(lst.size(), 2);
+  lst.insert("key", "new value", 1);
+  EXPECT_EQ(lst.size(), 2);
+  np = lst.search("key");
+  EXPECT_EQ(np->value, "new value");
+}
+
+TEST(SkipList, InsertLargeAmount) {
+  auto lst = SkipList<std::string, std::string>(std::less<std::string>());
+  const int N = 1 << 10;
+  for (int i = 1; i <= N; i++) {
+    std::string key = "key" + std::to_string(i);
+    std::string value = "value" + std::to_string(i);
+    auto np = lst.insert(key, value);
+    EXPECT_EQ(np->value, value);
+  }
+  EXPECT_EQ(lst.size(), N);
+  auto it = lst.begin();
+  std::string prevK = it->key, prevV = it->value;
+  it++;
+  int c = 1;
+  for (; it != lst.end(); it++) {
+    c++;
+    EXPECT_LT(prevK, it->key);
+    EXPECT_LT(prevV, it->value);
+  }
+  EXPECT_EQ(c, lst.size());
+}
+
+TEST(SkipList, Remove) {
+  auto lst = SkipList<std::string, std::string>(std::less<std::string>());
+  lst.insert("key", "value");
+  EXPECT_EQ(lst.size(), 1);
+  auto np = lst.search("key");
+  EXPECT_EQ(np->value, "value");
+
+  bool ret = lst.remove("key");
+  EXPECT_TRUE(ret);
+  EXPECT_EQ(lst.size(), 0);
+  np = lst.search("key");
+  EXPECT_EQ(np, nullptr);
+}
diff --git a/tests/test-vector.cc b/tests/test-vector.cc
index 3998c55..81c653f 100644
--- a/tests/test-vector.cc
+++ b/tests/test-vector.cc
@@ -1,4 +1,5 @@
 #include <gtest/gtest.h>
+
 #include "src/collections/vector.h"
 
 TEST(TestVec, TestSize) {