refactor: remove unnecessary using declarations and qualify std symbols

Replace global using declarations with explicit std:: qualifications.
Update ranges algorithms usage to std::ranges and fix permutation
iterator
offset to correctly handle 1-based k indexing.

3518/solution.cpp

@@ -4,25 +4,19 @@
 #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) {
+  std::string smallestPalindrome(std::string s, int k) {
 
-    string half = s.substr(0, s.size() / 2);
+    std::string half = s.substr(0, s.size() / 2);
 
-    sort(half);
+    std::ranges::sort(half);
 
-    set<string> permutations;
+    std::set<std::string> permutations;
 
     do {
       permutations.insert(half);
-    } while (next_permutation(half).found);
+    } while (std::ranges::next_permutation(half).found);
 
     if (permutations.size() > std::numeric_limits<int>::max()) {
       throw std::overflow_error("Number of permutations exceeds int limit");
@@ -30,14 +24,14 @@ public:
     int size = static_cast<int>(permutations.size());
 
     if (k > size) {
-      return string();
+      return std::string();
     }
 
     auto it = permutations.begin();
     advance(it, k - 1);
 
-    string mirroredHalf = *it;
+    std::string mirroredHalf = *it;
-    reverse(mirroredHalf);
+    std::ranges::reverse(mirroredHalf);
 
     return *it + mirroredHalf;
   }