🟢 Port problem 242 (Valid Anagram) from Swift to C++23

solutions/0201-0300/0242-valid-anagram/README.md

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+# 242. Valid Anagram
+
+[LeetCode problem 242](https://leetcode.com/problems/valid-anagram/)
+
+- **Difficulty**: Easy
+- **Tags**: hash-table, string, sorting
+
+## Description
+
+Given two strings `s` and `t`, return `true` if `t` is an anagram of `s`
+(uses the exact same letters, same counts), `false` otherwise.

solutions/0201-0300/0242-valid-anagram/solution.cpp

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+#include "solution.hpp"
+
+#include <algorithm>
+#include <array>
+#include <unordered_map>
+
+namespace leetcode::p0242 {
+
+bool solve(const std::string& s, const std::string& t) {
+    if (s.size() != t.size()) {
+        return false;
+    }
+
+    std::array<int, 26> counts{};
+
+    for (char c : s) {
+        ++counts.at(static_cast<std::size_t>(c - 'a'));
+    }
+    for (char c : t) {
+        --counts.at(static_cast<std::size_t>(c - 'a'));
+    }
+
+    return std::ranges::all_of(counts, [](int count) { return count == 0; });
+}
+
+bool solveHashMap(const std::string& s, const std::string& t) {
+    if (s.size() != t.size()) {
+        return false;
+    }
+
+    std::unordered_map<char, int> countS;
+    std::unordered_map<char, int> countT;
+
+    for (char c : s) {
+        ++countS[c];
+    }
+    for (char c : t) {
+        ++countT[c];
+    }
+
+    return countS == countT;
+}
+
+} // namespace leetcode::p0242

solutions/0201-0300/0242-valid-anagram/solution.hpp

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+#pragma once
+
+#include <string>
+
+namespace leetcode::p0242 {
+
+// optimized: O(n) time, O(1) space — fixed 26-slot count array (assumes
+// lowercase English letters, per the problem's constraints).
+bool solve(const std::string& s, const std::string& t);
+
+// hash-map: O(n) time, O(k) space (k = distinct characters) — works for any
+// character set, not just lowercase English letters.
+bool solveHashMap(const std::string& s, const std::string& t);
+
+} // namespace leetcode::p0242

solutions/0201-0300/0242-valid-anagram/test.cpp

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+#include <catch2/catch_test_macros.hpp>
+
+#include "solution.hpp"
+
+TEST_CASE("Problem 242 - optimized", "[p0242]") {
+    CHECK(leetcode::p0242::solve("anagram", "nagaram"));
+    CHECK_FALSE(leetcode::p0242::solve("rat", "car"));
+}
+
+TEST_CASE("Problem 242 - hash map", "[p0242]") {
+    CHECK(leetcode::p0242::solveHashMap("anagram", "nagaram"));
+    CHECK_FALSE(leetcode::p0242::solveHashMap("rat", "car"));
+}