diff --git a/2201/220119-CN.cpp b/2201/220119-CN.cpp
new file mode 100644
index 0000000..495acea
--- /dev/null
+++ b/2201/220119-CN.cpp
@@ -0,0 +1,102 @@
+#include <vector>
+#include <unordered_map>
+#include <unordered_set>
+#include <iostream>
+
+/**
+ * Optimising is some sort of art.
+ *
+ * 219. Contains Duplicate II
+ * Given an integer array nums and an integer k, return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k.
+ */
+
+struct Node {
+	int val;
+	Node* next;
+	explicit Node(int v, Node* n = nullptr) : val(v), next(n) {}
+	~Node() { delete this->next; }
+};
+
+class Solution {
+public:
+	static bool containsNearbyDuplicate(const std::vector<int>& nums, int k) {
+		Node* hashTable[65536] {};
+		int n = nums.size();
+		if (!(k = std::min(k, n))) return false;
+		int ni, nik;
+		for (int i = 0; i < k; ++i) {
+			ni = nums[i];
+			for (auto* ptr = hashTable[ni & 0xFFFF]; ptr; ptr = ptr->next) {
+				if (ptr->val == ni) {
+					for (auto*& j : hashTable)
+						delete j;
+					return true;
+				}
+			}
+			hashTable[ni & 0xFFFF] = new Node(ni, hashTable[ni & 0xFFFF]);
+		}
+		for (int i = k; i < n; ++i) {
+			ni = nums[i];
+			nik = nums[i - k];
+			for (auto* ptr = hashTable[ni & 0xFFFF]; ptr; ptr = ptr->next) {
+				if (ptr->val == ni) {
+					for (auto*& j : hashTable)
+						delete j;
+					return true;
+				}
+			}
+			hashTable[ni & 0xFFFF] = new Node(ni, hashTable[ni & 0xFFFF]);
+			for (auto ptr = hashTable[nik & 0xFFFF], prev = (decltype(ptr))(nullptr); ptr; (prev = ptr), (ptr = ptr->next)) {
+				if (ptr->val == nik) {
+					if (prev)
+						prev->next = ptr->next;
+					else
+						hashTable[nik & 0xFFFF] = ptr->next;
+					delete ptr;
+					break;
+				}
+			}
+		}
+		return false;
+	}
+};
+
+int main() {
+	std::cout << Solution::containsNearbyDuplicate({1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 15);
+	return 0;
+}
+
+class SolutionOld {
+public:
+	static bool containsNearbyDuplicate(const std::vector<int>& nums, int k) {
+		std::unordered_set<int> s;
+		int n = nums.size();
+		k = std::min(k, n);
+		for (int i = 0; i < k; ++i) {
+			if (s.count(nums[i]))
+				return true;
+			s.insert(nums[i]);
+		}
+		for (int i = k; i < n; ++i) {
+			if (s.count(nums[i]))
+				return true;
+			s.insert(nums[i]);
+			s.erase(nums[i - k]);
+		}
+		return false;
+	}
+};
+
+class SolutionOlder {
+public:
+	static bool containsNearbyDuplicate(const std::vector<int>& nums, int k) {
+		std::unordered_map<int, int> m;
+		int n = nums.size();
+		for (int i = 0; i < n; ++i) {
+			if (m.count(nums[i]) && i - m[nums[i]] <= k)
+				return true;
+			m[nums[i]] = i;
+		}
+		return false;
+	}
+};
diff --git a/2201/CMakeLists.txt b/2201/CMakeLists.txt
index 70d671a..e8b11d3 100644
--- a/2201/CMakeLists.txt
+++ b/2201/CMakeLists.txt
@@ -3,4 +3,4 @@ PROJECT(2201)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2201 220118.cpp)
\ No newline at end of file
+ADD_EXECUTABLE(2201 220119-CN.cpp)
\ No newline at end of file