二分查找 binary_search() 应用解析(详细)

binary_search() 判断target是否存在

binary_search() 在排序（正序）中，返回是否找到目标值（true or false）

定义和实现

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);

template <class ForwardIterator, class T>
  bool binary_search (ForwardIterator first, ForwardIterator last, const T& val)
{
   
	//Return iterator to lower bound 
	// 返回第一大于等于目标值得迭代器
	first = std::lower_bound(first, last, val);  
	return (first != last && !(val < *first));
}

实例：

// binary_search example
#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