diff --git a/clojure/709.clj b/clojure/709.clj
deleted file mode 100644
index ee38733..0000000
--- a/clojure/709.clj
+++ /dev/null
@@ -1,19 +0,0 @@
-(ns clojure.709
-  (:require [clojure.string :as str]
-            [clojure.test :refer [deftest is run-tests]]))
-
-(defn to-lower-case [s]
-  (str/lower-case s))
-
-(def resultado (to-lower-case "HELLO"))
-
-(println resultado)
-
-(deftest test-to-lower-case
-  (is (= "hello" (to-lower-case "HELLO")))
-  (is (= "world" (to-lower-case "world")))
-  (is (= "clojure" (to-lower-case "CloJure")))
-  (is (= "" (to-lower-case "")))
-  (is (= "123!@#" (to-lower-case "123!@#"))))
-
-(run-tests)
diff --git a/solutions/0701-0800/0709-to-lower-case/README.md b/solutions/0701-0800/0709-to-lower-case/README.md
new file mode 100644
index 0000000..49ac8d5
--- /dev/null
+++ b/solutions/0701-0800/0709-to-lower-case/README.md
@@ -0,0 +1,11 @@
+# 709. To Lower Case
+
+[LeetCode problem 709](https://leetcode.com/problems/to-lower-case/)
+
+- **Difficulty**: Easy
+- **Tags**: string
+
+## Description
+
+Given a string `s`, return the string after converting every uppercase
+letter to lowercase.
diff --git a/solutions/0701-0800/0709-to-lower-case/solution.cpp b/solutions/0701-0800/0709-to-lower-case/solution.cpp
new file mode 100644
index 0000000..f14275f
--- /dev/null
+++ b/solutions/0701-0800/0709-to-lower-case/solution.cpp
@@ -0,0 +1,14 @@
+#include "solution.hpp"
+
+#include <algorithm>
+#include <cctype>
+
+namespace leetcode::p0709 {
+
+std::string solve(std::string s) {
+    std::ranges::transform(
+        s, s.begin(), [](unsigned char c) { return static_cast<char>(std::tolower(c)); });
+    return s;
+}
+
+} // namespace leetcode::p0709
diff --git a/solutions/0701-0800/0709-to-lower-case/solution.hpp b/solutions/0701-0800/0709-to-lower-case/solution.hpp
new file mode 100644
index 0000000..e30b0fd
--- /dev/null
+++ b/solutions/0701-0800/0709-to-lower-case/solution.hpp
@@ -0,0 +1,11 @@
+#pragma once
+
+#include <string>
+
+namespace leetcode::p0709 {
+
+// optimized: O(n) time, O(n) space — map each character through
+// std::tolower.
+std::string solve(std::string s);
+
+} // namespace leetcode::p0709
diff --git a/solutions/0701-0800/0709-to-lower-case/test.cpp b/solutions/0701-0800/0709-to-lower-case/test.cpp
new file mode 100644
index 0000000..4c2eec9
--- /dev/null
+++ b/solutions/0701-0800/0709-to-lower-case/test.cpp
@@ -0,0 +1,11 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include "solution.hpp"
+
+TEST_CASE("Problem 709", "[p0709]") {
+    CHECK(leetcode::p0709::solve("HELLO") == "hello");
+    CHECK(leetcode::p0709::solve("world") == "world");
+    CHECK(leetcode::p0709::solve("CloJure") == "clojure");
+    CHECK(leetcode::p0709::solve("") == "");
+    CHECK(leetcode::p0709::solve("123!@#") == "123!@#");
+}