STL 源代码分析 算法 stl_algo.h -- binary_search

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binary_search

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描写叙述：利用 lower_bound 实现二分查找，返回 bool

源代码：

//version 1
template <class ForwardIterator, class T>
bool binary_search(ForwardIterator first, ForwardIterator last,
                   const T& value) {
  ForwardIterator i = lower_bound(first, last, value);
  return i != last && !(value < *i);
}
//version 2
template <class ForwardIterator, class T, class Compare>
bool binary_search(ForwardIterator first, ForwardIterator last, const T& value,
                   Compare comp) {
  ForwardIterator i = lower_bound(first, last, value, comp);
  return i != last && !comp(value, *i);
}

演示样例：

int main()
{
  int A[] = { 1, 2, 3, 3, 3, 5, 8 };
  const int N = sizeof(A) / sizeof(int);

  for (int i = 1; i <= 10; ++i) {
    cout << "Searching for " << i << ": "
         << (binary_search(A, A + N, i) ? "present" : "not present") << endl;
  }
}
/*
The output is:
Searching for 1: present
Searching for 2: present
Searching for 3: present
Searching for 4: not present
Searching for 5: present
Searching for 6: not present
Searching for 7: not present
Searching for 8: present
Searching for 9: not present
Searching for 10: not present
*/

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