diff --git a/cpp/2305/LC230503CN.cpp b/cpp/2305/LC230503CN.cpp
new file mode 100644
index 0000000..504a92c
--- /dev/null
+++ b/cpp/2305/LC230503CN.cpp
@@ -0,0 +1,44 @@
+#include <string>
+
+/**
+ * 1003. Check If Word Is Valid After Substitutions
+ *
+ * Given a string s, determine if it is valid.
+ *
+ * A string s is valid if, starting with an empty string t = "", you can transform t into s after performing the following operation any number of times:
+ *
+ * Insert string "abc" into any position in t. More formally, t becomes t[left] + "abc" + t[right], where t == t[left] + t[right]. Note that t[left] and t[right] may be empty.
+ * Return true if s is a valid string, otherwise, return false.
+ */
+
+
+class LC230503CN {
+public:
+	static bool isValid(const std::string&) noexcept;
+};
+
+int matcher(const char* str) noexcept {
+	auto* ptr = str;
+	for (int i = 0; i < 3;) {
+		if (i + 'a' == *str) {
+			// Advance
+			++str;
+			++i;
+		} else if ('a' == *str) {
+			int adv = matcher(str);
+			if (!adv)
+				return 0;
+			str += adv;
+		} else return 0;
+	}
+	return str - ptr;
+}
+
+bool LC230503CN::isValid(const std::string& s) noexcept {
+	for (auto* ptr = s.c_str(); *ptr;)
+		if (int adv = matcher(ptr); adv)
+			ptr += adv;
+		else
+			return false;
+	return true;
+}
diff --git a/cpp/2305/defs.h b/cpp/2305/defs.h
index f6a9f69..0ddf4d3 100644
--- a/cpp/2305/defs.h
+++ b/cpp/2305/defs.h
@@ -24,4 +24,9 @@ public:
 	static int arraySign(const std::vector<int>&) noexcept;
 };
 
+class LC230503CN {
+public:
+	static bool isValid(const std::string&) noexcept;
+};
+
 #endif //LEETCODE_CPP_DEFS_H
diff --git a/cpp/2305/main.cpp b/cpp/2305/main.cpp
index 53e8086..5cdba9c 100644
--- a/cpp/2305/main.cpp
+++ b/cpp/2305/main.cpp
@@ -12,8 +12,6 @@ std::ostream& operator<<(std::ostream& os, const std::vector<T>& x) noexcept {
 }
 
 int main() {
-	std::cout << LC230501::average({1, 2, 3, 4}) << std::endl;
-	std::cout << LC230501CN::numOfMinutes(1, 0, {-1}, {0}) << std::endl;
-	std::cout << LC230502CN::powerfulIntegers(2, 1, 10) << std::endl;
+	std::cout << LC230503CN::isValid("aabbcc");
 	return 0;
 }