本文为senlie原创，转载请保留此地址：http://blog.csdn.net/zhengsenlie
equal_range(应用于有序区间)
--------------------------------------------------------------------------------------------------------------------------------------
描写叙述：利用二分查找找到一个区间，区间里的全部值都等于给定值，返回的是一个pair。
分别存储区间的上界迭代器和下界迭代器
源代码：
template <class ForwardIterator, class T>
inline pair<ForwardIterator, ForwardIterator>
equal_range(ForwardIterator first, ForwardIterator last, const T& value) {
return __equal_range(first, last, value, distance_type(first),
iterator_category(first));
} // ForwardIterator 版本号
template <class ForwardIterator, class T, class Distance>
pair<ForwardIterator, ForwardIterator>
__equal_range(ForwardIterator first, ForwardIterator last, const T& value,
Distance*, forward_iterator_tag) {
Distance len = 0;
distance(first, last, len);
Distance half;
ForwardIterator middle, left, right; while (len > 0) { // 奇怪？ 为什么不直接用 lower_bound 、 upper_bound ， 而是等找到值再用？
// --> 我认为是效率方面的考虑。 先找 value ，这时左右两个区间可能已经缩小了很多。
// 再利用 lower_bound 和 upper_bound 代价小非常多
half = len >> 1;
middle = first;
advance(middle, half);
if (*middle < value) {
first = middle;
++first;
len = len - half - 1;
}
else if (value < *middle)
len = half;
else {
left = lower_bound(first, middle, value);
advance(first, len);
right = upper_bound(++middle, first, value);
return pair<ForwardIterator, ForwardIterator>(left, right);
}
}
return pair<ForwardIterator, ForwardIterator>(first, first);
} // RandomAccessIterator 版本号
template <class RandomAccessIterator, class T, class Distance>
pair<RandomAccessIterator, RandomAccessIterator>
__equal_range(RandomAccessIterator first, RandomAccessIterator last,
const T& value, Distance*, random_access_iterator_tag) {
Distance len = last - first;
Distance half;
RandomAccessIterator middle, left, right; while (len > 0) {
half = len >> 1;
middle = first + half;
if (*middle < value) {
first = middle + 1;
len = len - half - 1;
}
else if (value < *middle)
len = half;
else {
left = lower_bound(first, middle, value);
right = upper_bound(++middle, first + len, value);
return pair<RandomAccessIterator, RandomAccessIterator>(left,
right);
}
}
return pair<RandomAccessIterator, RandomAccessIterator>(first, first);
}
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 = 2; i <= 4; ++i) {
pair<int*, int*> result = equal_range(A, A + N, i); cout << endl;
cout << "Searching for " << i << endl;
cout << " First position where " << i << " could be inserted: "
<< result.first - A << endl;
cout << " Last position where " << i << " could be inserted: "
<< result.second - A << endl;
if (result.first < A + N)
cout << " *result.first = " << *result.first << endl;
if (result.second < A + N)
cout << " *result.second = " << *result.second << endl;
}
}
/*
The output is:
Searching for 2
First position where 2 could be inserted: 1
Last position where 2 could be inserted: 2
*result.first = 2
*result.second = 3 Searching for 3
First position where 3 could be inserted: 2
Last position where 3 could be inserted: 5
*result.first = 3
*result.second = 5 Searching for 4
First position where 4 could be inserted: 5
Last position where 4 could be inserted: 5
*result.first = 5
*result.second = 5*/