[cpp][12_sorts] inplace_merge_sort, impl inplace_merge manually.

Author: Liam0205

c-cpp/12_sorts/merge_sort.hpp

@@ -31,6 +31,17 @@ OutputIt merge(InputIt1 first1, InputIt1 last1,
  }
  return std::copy(first2, last2, d_first);
 }
+
+template <typename FrwdIt,
+ typename BinaryPred = std::less<typename std::iterator_traits<FrwdIt>::value_type>>
+void inplace_merge(FrwdIt first, FrwdIt middle, FrwdIt last, BinaryPred comp = BinaryPred()) {
+ // with sufficient memory space
+ const auto len = std::distance(first, last);
+ std::vector<typename std::iterator_traits<FrwdIt>::value_type> tmp;
+ tmp.reserve(len);
+ detail::merge(first, middle, middle, last, std::back_inserter(tmp), comp);
+ std::copy(tmp.begin(), tmp.end(), first);
+}
 } // namespace detail
 
 template <typename FrwdIt,