thrust::pair<ForwardIterator, ForwardIterator> thrust::equal_range	(	ForwardIterator	first,
		ForwardIterator	last,
		const T &	value,
		StrictWeakOrdering	comp
	)

equal_range is a version of binary search: it attempts to find the element value in an ordered range [first, last). The value returned by equal_range is essentially a combination of the values returned by lower_bound and upper_bound: it returns a pair of iterators i and j such that i is the first position where value could be inserted without violating the ordering and j is the last position where value could be inserted without violating the ordering. It follows that every element in the range [i, j) is equivalent to value, and that [i, j) is the largest subrange of [first, last) that has this property.

This version of equal_range returns a pair of iterators [i, j). i is the furthermost iterator in [first, last) such that, for every iterator k in [first, i), comp(*k, value) is true. j is the furthermost iterator in [first, last) such that, for every iterator k in [first, last), comp(value, *k) is false. For every iterator k in [i, j), neither comp(value, *k) nor comp(*k, value) is true.

Parameters

first	The beginning of the ordered sequence.
last	The end of the ordered sequence.
value	The value to be searched.
comp	The comparison operator.

Returns: A pair of iterators [i, j) that define the range of equivalent elements.

Template Parameters

ForwardIterator	is a model of Forward Iterator.
T	is comparable to `ForwardIterator's` `value_type`.
StrictWeakOrdering	is a model of Strict Weak Ordering.

The following code snippet demonstrates how to use equal_range to search for values in a ordered range.

#include <thrust/binary_search.h>
#include <thrust/device_vector.h>
#include <thrust/functional.h>
...
thrust::device_vector<int> input(5);
input[0] = 0;
input[1] = 2;
input[2] = 5;
input[3] = 7;
input[4] = 8;
thrust::equal_range(input.begin(), input.end(), 0, thrust::less<int>()); // returns [input.begin(), input.begin() + 1)
thrust::equal_range(input.begin(), input.end(), 1, thrust::less<int>()); // returns [input.begin() + 1, input.begin() + 1)
thrust::equal_range(input.begin(), input.end(), 2, thrust::less<int>()); // returns [input.begin() + 1, input.begin() + 2)
thrust::equal_range(input.begin(), input.end(), 3, thrust::less<int>()); // returns [input.begin() + 2, input.begin() + 2)
thrust::equal_range(input.begin(), input.end(), 8, thrust::less<int>()); // returns [input.begin() + 4, input.end)
thrust::equal_range(input.begin(), input.end(), 9, thrust::less<int>()); // returns [input.end(), input.end)

See also: https://en.cppreference.com/w/cpp/algorithm/equal_range; lower_bound; upper_bound; binary_search