🟢 Port problem 1768 (Merge Strings Alternately) from Ruby to C++23

solutions/1701-1800/1768-merge-strings-alternately/README.md

@@ -0,0 +1,12 @@
+# 1768. Merge Strings Alternately
+
+[LeetCode problem 1768](https://leetcode.com/problems/merge-strings-alternately/)
+
+- **Difficulty**: Easy
+- **Tags**: two-pointers, string
+
+## Description
+
+Given two strings `word1` and `word2`, merge them by adding letters in
+alternating order, starting with `word1`. Once one string runs out, append
+the remaining letters of the other.

solutions/1701-1800/1768-merge-strings-alternately/solution.cpp

@@ -0,0 +1,23 @@
+#include "solution.hpp"
+
+namespace leetcode::p1768 {
+
+std::string solve(const std::string& word1, const std::string& word2) {
+    std::string result;
+    result.reserve(word1.size() + word2.size());
+
+    std::size_t i = 0;
+    while (i < word1.size() || i < word2.size()) {
+        if (i < word1.size()) {
+            result += word1[i];
+        }
+        if (i < word2.size()) {
+            result += word2[i];
+        }
+        ++i;
+    }
+
+    return result;
+}
+
+} // namespace leetcode::p1768

solutions/1701-1800/1768-merge-strings-alternately/solution.hpp

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <string>
+
+namespace leetcode::p1768 {
+
+// optimized: O(n + m) time, O(n + m) space — walk both strings once.
+std::string solve(const std::string& word1, const std::string& word2);
+
+} // namespace leetcode::p1768

solutions/1701-1800/1768-merge-strings-alternately/test.cpp

@@ -0,0 +1,11 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include "solution.hpp"
+
+TEST_CASE("Problem 1768", "[p1768]") {
+    CHECK(leetcode::p1768::solve("abc", "pqr") == "apbqcr");
+    CHECK(leetcode::p1768::solve("ab", "pqrs") == "apbqrs");
+    CHECK(leetcode::p1768::solve("abcd", "pq") == "apbqcd");
+    CHECK(leetcode::p1768::solve("", "") == "");
+    CHECK(leetcode::p1768::solve("abc", "") == "abc");
+}