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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

*/