diff --git a/cpp/2210/221030-CN.cpp b/cpp/2210/221030-CN.cpp
new file mode 100644
index 0000000..db540d9
--- /dev/null
+++ b/cpp/2210/221030-CN.cpp
@@ -0,0 +1,31 @@
+#include <vector>
+#include <functional>
+#include <cctype>
+
+/**
+ * 784. Letter Case Permutation
+ *
+ * Given a string s, you can transform every letter individually to be lowercase or uppercase to create another string.
+ * Return a list of all possible strings we could create. Return the output in any order.
+ */
+
+class Solution {
+public:
+	std::vector<std::string> letterCasePermutation(std::string& s) {
+		std::vector<std::string> ret;
+		std::function<void(int)> f = [&](int pos) {
+			if (pos >= s.length()) {
+				ret.push_back(s);
+			} else if (std::isalpha(s[pos])) {
+				s[pos] = std::tolower(s[pos]);
+				f(1 + pos);
+				s[pos] = std::toupper(s[pos]);
+				f(1 + pos);
+			} else {
+				f(1 + pos);
+			}
+		};
+		f(0);
+		return ret;
+	}
+};