[cpp][15_bsearch] done.

Author: Liam0205

c-cpp/15_bsearch/bsearch.hpp

@@ -0,0 +1,62 @@
+/**
+ * Created by Liam Huang (Liam0205) on 2018/10/24.
+ */
+
+#ifndef BSEARCH_BSEARCH_HPP_
+#define BSEARCH_BSEARCH_HPP_
+
+#include <iterator>
+#include <functional>
+
+enum class BsearchPolicy { FIRST, LAST, UNSPECIFIED };
+
+template <typename IterT,
+          typename ValueT = typename std::iterator_traits<IterT>::value_type,
+          typename Compare = std::less<ValueT>>
+IterT bsearch(IterT first,
+              IterT last,
+             ValueT target,
+            Compare comp,
+      BsearchPolicy policy = BsearchPolicy::UNSPECIFIED) {
+    IterT result = last;
+    while (std::distance(first, last) > 0) {
+        IterT mid = first + std::distance(first, last) / 2;
+        if (comp(*mid, target)) {
+            first = mid + 1;
+        } else if (comp(target, *mid)) {
+            last = mid;
+        } else {  // equal
+            if (policy == BsearchPolicy::FIRST) {
+                if (mid == first or comp(*(mid - 1), *mid)) {
+                    result = mid;
+                    break;
+                } else {
+                    last = mid;
+                }
+            } else if (policy == BsearchPolicy::LAST) {
+                if (std::distance(mid, last) == 1 or comp(*mid, *(mid + 1))) {
+                    result = mid;
+                    break;
+                } else {
+                    first = mid + 1;
+                }
+            } else {
+                result = mid;
+                break;
+            }
+        }
+    }
+    return result;
+}
+
+template <typename IterT,
+          typename ValueT = typename std::iterator_traits<IterT>::value_type>
+IterT bsearch(IterT first,
+              IterT last,
+             ValueT target,
+      BsearchPolicy policy = BsearchPolicy::UNSPECIFIED) {
+	return bsearch(first, last, target, std::less<ValueT>(), policy);
+}
+
+#endif  // BSEARCH_BSEARCH_HPP_
+

c-cpp/15_bsearch/bsearch_test.cc

@@ -0,0 +1,38 @@
+/**
+ * Created by Liam Huang (Liam0205) on 2018/10/24.
+ */
+
+#include <iostream>
+#include <vector>
+
+#include "bsearch.hpp"
+
+template <typename VecT, typename T = typename VecT::value_type>
+void test_bsearch(const VecT& test,
+                            T target,
+                BsearchPolicy policy = BsearchPolicy::UNSPECIFIED) {
+    auto it = bsearch(test.begin(), test.end(), target, policy);
+    std::cout << std::distance(test.begin(), it) << std::endl;
+}
+
+int main() {
+    std::vector<int> test{0, 0, 1, 2, 3, 4, 4, 5, 5, 5, 5, 5, 6, 7};  // std::less<int>()
+
+    test_bsearch(test, 8);                        // 14
+    test_bsearch(test, -1);                       // 14
+    test_bsearch(test, 0);                        // 0, 1
+    test_bsearch(test, 0, BsearchPolicy::FIRST);  // 0
+    test_bsearch(test, 0, BsearchPolicy::LAST);   // 1
+    test_bsearch(test, 4);                        // 5, 6
+    test_bsearch(test, 4, BsearchPolicy::FIRST);  // 5
+    test_bsearch(test, 4, BsearchPolicy::LAST);   // 6
+    test_bsearch(test, 5);                        // 7, 8, 9, 10, 11
+    test_bsearch(test, 5, BsearchPolicy::FIRST);  // 7
+    test_bsearch(test, 5, BsearchPolicy::LAST);   // 11
+    test_bsearch(test, 7);                        // 13
+    test_bsearch(test, 7, BsearchPolicy::FIRST);  // 13
+    test_bsearch(test, 7, BsearchPolicy::LAST);   // 13
+
+    return 0;
+}
+