binary_search-优快云博客

本文链接：https://blog.youkuaiyun.com/zhu2695/article/details/8830823

本文介绍C++标准库中binary_search函数的应用，展示了如何使用默认比较及自定义比较函数进行二分查找，并通过示例代码解释了其工作原理。

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/**binary_search 实现二分查找，如果是随机存取迭代器，则是对数复杂度，否则为线性复杂度。
*  要求目标区间已排序。
*/

/**
  template <class ForwardIterator, class T>
  bool binary_search (ForwardIterator first, ForwardIterator last,
                      const T& val);
 
  template <class ForwardIterator, class T, class Compare>
  bool binary_search (ForwardIterator first, ForwardIterator last,
                      const T& val, Compare comp); 
*/

#include <iostream>     // std::cout
#include <algorithm>    // std::binary_search, std::sort
#include <vector>       // std::vector

bool myfunction (int i,int j) { return (i<j); }

int main () {
  int myints[] = {1,2,3,4,5,4,3,2,1};
  std::vector<int> v(myints,myints+9);                         // 1 2 3 4 5 4 3 2 1

  // using default comparison:
  std::sort (v.begin(), v.end());

  std::cout << "looking for a 3... ";
  if (std::binary_search (v.begin(), v.end(), 3))
    std::cout << "found!\n"; else std::cout << "not found.\n";

  // using myfunction as comp:
  std::sort (v.begin(), v.end(), myfunction);

  std::cout << "looking for a 6... ";
  if (std::binary_search (v.begin(), v.end(), 6, myfunction))
    std::cout << "found!\n"; else std::cout << "not found.\n";

  system("pause");
  return 0;
}

/*
Output:

looking for a 3... found!
looking for a 6... not found.
*/