feat: add solution for smallest palindromic rearrangement ii

- add problem 3518 implementation
- add build configuration with debug and release modes
- add test cases and examples
- add makefile for problem-specific build workflow

3518/main.cpp

@@ -0,0 +1,59 @@
+#include "solution.cpp"
+
+#include <cassert>
+#include <iostream>
+
+int main(int argc, char *argv[]) {
+  (void)argc;
+  (void)argv;
+
+  Solution s;
+
+  // Example 1
+  {
+    std::string result = s.smallestPalindrome("abba", 2);
+    assert(result == "baab");
+  }
+
+  // Example 2
+  {
+    std::string result = s.smallestPalindrome("aa", 2);
+    assert(result == "");
+  }
+
+  // Example 3
+  {
+    std::string result = s.smallestPalindrome("bacab", 1);
+    assert(result == "abcba");
+  }
+
+  // Additional tests
+
+  // Single palindrome
+  {
+    std::string result = s.smallestPalindrome("aaa", 1);
+    assert(result == "aaa");
+  }
+
+  // k exceeds number of permutations
+  {
+    std::string result = s.smallestPalindrome("aabb", 3);
+    assert(result == "");
+  }
+
+  // Two different characters
+  {
+    std::string result = s.smallestPalindrome("aabbcc", 1);
+    assert(result == "abccba");
+  }
+
+  // Already sorted palindrome
+  {
+    std::string result = s.smallestPalindrome("abcba", 2);
+    assert(result == "bacab");
+  }
+
+  std::cout << "All tests passed!\n";
+
+  return 0;
+}