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/solution.cpp

@@ -0,0 +1,44 @@
+#include <algorithm>
+#include <limits>
+#include <set>
+#include <stdexcept>
+#include <string>
+
+using std::set;
+using std::string;
+using std::ranges::next_permutation;
+using std::ranges::reverse;
+using std::ranges::sort;
+
+class Solution {
+public:
+  string smallestPalindrome(string s, int k) {
+
+    string half = s.substr(0, s.size() / 2);
+
+    sort(half);
+
+    set<string> permutations;
+
+    do {
+      permutations.insert(half);
+    } while (next_permutation(half).found);
+
+    if (permutations.size() > std::numeric_limits<int>::max()) {
+      throw std::overflow_error("Number of permutations exceeds int limit");
+    }
+    int size = static_cast<int>(permutations.size());
+
+    if (k > size) {
+      return string();
+    }
+
+    auto it = permutations.begin();
+    advance(it, k);
+
+    string mirroredHalf = *it;
+    reverse(mirroredHalf);
+
+    return *it + mirroredHalf;
+  }
+};