thrust::equal_range

Defined in thrust/binary_search.h

template<class ForwardIterator, class T, class StrictWeakOrdering> 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.

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

lower_bound

See also

upper_bound

See also

Binary Search

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.

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.

Returns

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