[cpp][12_sorts] merge_sort, done.

Author: Liam0205

c-cpp/12_sorts/merge_sort.hpp

@@ -0,0 +1,51 @@
+/**
+ * Created by Liam Huang (Liam0205) on 2018/10/17.
+ */
+
+#ifndef SORTS_MERGE_SORT_HPP_
+#define SORTS_MERGE_SORT_HPP_
+
+#include <functional>
+#include <algorithm>
+#include <iterator>
+#include <vector>
+
+namespace detail {
+template <typename InputIt1, typename InputIt2, typename OutputIt,
+ typename BinaryPred = std::less<typename std::iterator_traits<InputIt1>::value_type>>
+OutputIt merge(InputIt1 first1, InputIt1 last1,
+ InputIt2 first2, InputIt2 last2,
+ OutputIt d_first,
+ BinaryPred comp = BinaryPred()) {
+ for (; first1 != last1; ++d_first) {
+ if (first2 == last2) {
+ return std::copy(first1, last1, d_first);
+ }
+ if (comp(*first2, *first1)) {
+ *d_first = *first2;
+ ++first2;
+ } else {
+ *d_first = *first1;
+ ++first1;
+ }
+ }
+ return std::copy(first2, last2, d_first);
+}
+} // namespace detail
+
+template <typename FrwdIt,
+ typename BinaryPred = std::less<typename std::iterator_traits<FrwdIt>::value_type>>
+void merge_sort(FrwdIt first, FrwdIt last, BinaryPred comp = BinaryPred()) {
+ const auto len = std::distance(first, last);
+ if (len <= 1) { return; }
+ auto cut = first + len / 2;
+ merge_sort(first, cut, comp);
+ merge_sort(cut, last, comp);
+ std::vector<typename std::iterator_traits<FrwdIt>::value_type> tmp;
+ tmp.reserve(len);
+ detail::merge(first, cut, cut, last, std::back_inserter(tmp), comp);
+ std::copy(tmp.begin(), tmp.end(), first);
+}
+
+#endif // SORTS_MERGE_SORT_HPP_
+

c-cpp/12_sorts/merge_sort_test.cc

@@ -0,0 +1,19 @@
+/**
+ * Created by Liam Huang (Liam0205) on 2018/10/17.
+ */
+
+#include <iostream>
+#include <vector>
+#include "merge_sort.hpp"
+
+int main() {
+ std::vector<int> test_data{0, -1, 3, 190, -500};
+ merge_sort(test_data.begin(), test_data.end());
+ for (auto i : test_data) {
+ std::cout << i << ' ';
+ }
+ std::cout << std::endl;
+
+ return 0;
+}
+