problems(cpp): add “1768. Merge Strings Alternately”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/merge-strings-alternately.cpp

@@ -0,0 +1,39 @@
+#include <cassert>
+#include <string>
+
+class Solution {
+public:
+    std::string mergeAlternately(const std::string& word1, const std::string& word2)
+    {
+        std::string result;
+
+        auto l = word1.begin();
+        auto r = word2.begin();
+
+        for (; l != word1.end() && r != word2.end(); ++l, ++r) {
+            result += *l;
+            result += *r;
+        }
+
+        for (; l != word1.end(); ++l) {
+            result += *l;
+        }
+
+        for (; r != word2.end(); ++r) {
+            result += *r;
+        }
+
+        return result;
+    }
+};
+
+int main()
+{
+    Solution s;
+
+    assert(s.mergeAlternately("abc", "pqr") == "apbqcr");
+    assert(s.mergeAlternately("ab", "pqrs") == "apbqrs");
+    assert(s.mergeAlternately("abcd", "pq") == "apbqcd");
+
+    return 0;
+}