diff --git a/cpp/2305/LC230520.cpp b/cpp/2305/LC230520.cpp
new file mode 100644
index 0000000..997579b
--- /dev/null
+++ b/cpp/2305/LC230520.cpp
@@ -0,0 +1,71 @@
+#include <queue>
+#include <string>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+
+/**
+ * 399. Evaluate Division
+ * You are given an array of variable pairs equations and an array of real numbers values, where equations[i] = [Ai, Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi is a string that represents a single variable.
+ * You are also given some queries, where queries[j] = [Cj, Dj] represents the jth query where you must find the answer for Cj / Dj = ?.
+ * Return the answers to all queries. If a single answer cannot be determined, return -1.0.
+ */
+
+class LC230520 {
+public:
+	template<typename T>
+	using V = std::vector<T>;
+	using VD = V<double>;
+	using CVVS = const V<V<std::string>>;
+
+	static VD calcEquation(CVVS&, const VD&, CVVS&) noexcept;
+};
+
+std::vector<double> LC230520::calcEquation(CVVS& equations, const VD& values, CVVS& queries) noexcept {
+	const int n = equations.size();
+	std::unordered_map<std::string, int> id_map;
+	std::unordered_map<int, std::unordered_map<int, double>> directed_map;
+	int cnt = 0;
+	for (int i = 0; i < n; ++i) {
+		for (int j = 0; j < 2; ++j)
+			if (!id_map.count(equations[i][j]))
+				id_map[equations[i][j]] = cnt++;
+		directed_map[id_map[equations[i][0]]][id_map[equations[i][1]]] = values[i];
+		directed_map[id_map[equations[i][1]]][id_map[equations[i][0]]] = 1.0 / values[i];
+	}
+	VD ret;
+	for (auto&& t : queries) {
+		if (!(id_map.count(t[0]) && id_map.count(t[1]))) {
+			ret.push_back(-1.0);
+			continue;
+		}
+		int numerator = id_map[t[0]], denominator = id_map[t[1]];
+		if (numerator == denominator) {
+			ret.push_back(1.0);
+			continue;
+		}
+		int vis = 1 << numerator;
+		bool found = false;
+		std::queue<std::pair<int, double>> q;
+		q.emplace(numerator, 1.0);
+		while (!q.empty()) {
+			auto [c, cr] = q.front();
+			for (auto [nc, ncr] : directed_map[c]) {
+				if (vis & (1 << nc))
+					continue;
+				vis |= 1 << nc;
+				if (nc == denominator) {
+					found = true;
+					ret.push_back(cr * ncr);
+					break;
+				}
+				q.emplace(nc, cr * ncr);
+			}
+			if (found)
+				break;
+		}
+		if (!found)
+			ret.push_back(-1);
+	}
+	return ret;
+}
diff --git a/cpp/2305/defs.h b/cpp/2305/defs.h
index 8ca2142..d683252 100644
--- a/cpp/2305/defs.h
+++ b/cpp/2305/defs.h
@@ -134,4 +134,14 @@ public:
 	static int countGoodStrings(int, int, int, int) noexcept;
 };
 
+class LC230520 {
+public:
+	template<typename T>
+	using V = std::vector<T>;
+	using VD = V<double>;
+	using CVVS = const V<V<std::string>>;
+
+	static VD calcEquation(CVVS&, const VD&, CVVS&) noexcept;
+};
+
 #endif //LEETCODE_CPP_DEFS_H
diff --git a/cpp/2305/main.cpp b/cpp/2305/main.cpp
index 08b49b3..cdddd58 100644
--- a/cpp/2305/main.cpp
+++ b/cpp/2305/main.cpp
@@ -1,4 +1,5 @@
 #include <cstdio>
+#include <exception>
 #include <iostream>
 #include <ostream>
 #include <unordered_set>
@@ -13,7 +14,44 @@ std::ostream& operator<<(std::ostream& os, const std::vector<T>& x) noexcept {
 	return os;
 }
 
+int* partition(int* L, int* R) {
+	int pivot = R - L;
+	std::swap(L[rand() % pivot], *R);
+	int pivot_index = 0;
+	for (int i = 0; i < pivot; ++i)
+		if (L[i] < *R)
+			std::swap(L[i], L[pivot_index++]);
+	std::swap(*R, L[pivot_index]);
+	return pivot_index + L;
+}
+
+void quick_sort(int* L, int* R) {
+	if (L >= R)
+		return;
+	if (R - L == 1) {
+		if (*L > *R)
+			std::swap(*L, *R);
+		return;
+	}
+	int* pivot = partition(L, R);
+	quick_sort(L, pivot - 1);
+	quick_sort(pivot + 1, R);
+}
+
+void heapify(int* L, int* R) {
+	int len = R - L + 1;
+	int* rs = L - 1;
+	for (int i = len; i; --i) {
+		if (rs[i] > rs[i >> 1])
+			std::swap(rs[i], rs[i >> 1]);
+	}
+}
+
 int main() {
-	std::cout << LC230513::countGoodStrings(2,3,1,2);
+	LC230520::calcEquation(
+		{{"a", "b"}, {"b", "c"}},
+		{2.0, 3.0},
+		{{"a", "c"}, {"b", "a"}}
+	);
 	return 0;
 }