diff --git a/2201/CMakeLists.txt b/2201/CMakeLists.txt
index 768abbd..a3a4c87 100644
--- a/2201/CMakeLists.txt
+++ b/2201/CMakeLists.txt
@@ -3,4 +3,4 @@ PROJECT(2201)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2201 220131.cpp)
+ADD_EXECUTABLE(2201 220129.cpp)
diff --git a/2202/220201-CN.cpp b/2202/220201-CN.cpp
index 9716994..54214c8 100644
--- a/2202/220201-CN.cpp
+++ b/2202/220201-CN.cpp
@@ -1,8 +1,39 @@
 #include <string>
+#include <cctype>
+#include <cstdio>
 
 class Solution {
+private:
+	static bool isNice(const std::string& str, int L, int R) {
+		bool bucket[2][26]{};
+		for (int i = L; i < R; ++i)
+			*(std::isupper(str[i]) ? &bucket[0][str[i] - 'A'] : &bucket[1][str[i] - 'a']) = true;
+		for (int i = 0; i < 26; ++i)
+			if ((bucket[0][i] || bucket[1][i]) && !(bucket[0][i] && bucket[1][i]))
+				return false;
+		return true;
+	}
 public:
-    std::string longestNiceSubstring(const std::string& s) {
-
+    static std::string longestNiceSubstring(const std::string& s) {
+		const int n = s.length();
+		std::string ret;
+		int retMax = 0;
+		for (int i = 0; i < n; ++i) {
+			for (int j = i + 1; j <= n; ++j) {
+				if (j - i > retMax && isNice(s, i, j)) {
+					retMax = j - i;
+					ret = s.substr(i, j - i);
+				}
+			}
+		}
+		return ret;
     }
-};
\ No newline at end of file
+};
+
+int main() {
+	std::printf("%s\n", Solution::longestNiceSubstring("YazaAay").c_str());
+	std::printf("%s\n", Solution::longestNiceSubstring("Bb").c_str());
+	std::printf("%s\n", Solution::longestNiceSubstring("c").c_str());
+	std::printf("%s\n", Solution::longestNiceSubstring("dDzeE").c_str());
+	return 0;
+}