Merge pull request wangzheng0822#97 from Liam0205/15_bsearch

[cpp][15_bsearch] 实现带搜索策略的二分查找

Author: wangzheng0822

c-cpp/15_bsearch/.gitkeep

@@ -0,0 +1,66 @@
+/**
+ * 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 };
+
+// Liam Huang: The algorithm works right with iterators that meet the ForwardIterator requirement,
+// but with a bad time complexity. For better performance, iterators should meet
+// the RandomAccessIterator requirement.
+template <typename IterT,
+ typename ValueT = typename std::iterator_traits<IterT>::value_type,
+ typename Compare>
+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,
+ typename Compare = std::less<ValueT>>
+IterT bsearch(IterT first,
+ IterT last,
+ ValueT target,
+ BsearchPolicy policy = BsearchPolicy::UNSPECIFIED) {
+return bsearch(first, last, target, Compare(), policy);
+}
+
+#endif // BSEARCH_BSEARCH_HPP_
+

c-cpp/15_bsearch/bsearch.hpp

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+/**
+ * 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;
+}
+