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Difference between revisions of "cpp/algorithm/exclusive scan"

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{{par | binary_op | binary {{named req|FunctionObject}} that will be applied in to the result of dereferencing the input iterators, the results of other {{tt|binary_op}}, and {{tt|init}}.}}
 
{{par | binary_op | binary {{named req|FunctionObject}} that will be applied in to the result of dereferencing the input iterators, the results of other {{tt|binary_op}}, and {{tt|init}}.}}
 
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{{par req concept | T | MoveConstructible | notes=and {{tt|binary_op(init, *first)}}, {{tt|binary_op(init, init)}}, and {{tt|binary_op(*first, *first)}} must be convertible to {{tt|T}}}}
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{{par req named | T | MoveConstructible | notes=and {{tt|binary_op(init, *first)}}, {{tt|binary_op(init, init)}}, and {{tt|binary_op(*first, *first)}} must be convertible to {{tt|T}}}}
 
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Revision as of 15:15, 15 June 2018

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
(C++17)   
exclusive_scan
(C++17)
Operations on uninitialized memory
 
Defined in header <numeric>
template< class InputIt, class OutputIt, class T >

OutputIt exclusive_scan( InputIt first, InputIt last,

                         OutputIt d_first, T init );
 (1) (since C++17)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T >

ForwardIt2 exclusive_scan( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last,

                           ForwardIt2 d_first, T init);
 (2) (since C++17)
template< class InputIt, class OutputIt,

          class T, class BinaryOperation >
OutputIt exclusive_scan( InputIt first, InputIt last,

                         OutputIt d_first, T init, BinaryOperation binary_op );
 (3) (since C++17)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,

          class T, class BinaryOperation >
ForwardIt2 exclusive_scan( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last,

                           ForwardIt2 d_first, T init, BinaryOperation binary_op );
 (4) (since C++17)

Computes an exclusive prefix sum operation using binary_op (or std::plus<>() for overloads (1-2)) for the range [first, last), using init as the initial value, and writes the results to the range beginning at d_first. "exclusive" means that the i-th input element is not included in the i-th sum.

Formally, assigns through each iterator i in [d_first, d_first + (last - first)) the value of the generalized noncommutative sum of init, *j... for every j in [first, first + (i - d_first)) over binary_op,

where generalized noncommutative sum GNSUM(op, a1, ..., aN) is defined as follows:

  • if N=1, a1
  • if N > 1, op(GNSUM(op, a1, ..., aK), GNSUM(op, aM, ..., aN)) for any K where 1 < K+1 = M ≤ N

In other words, the summation operations may be performed in arbitrary order, and the behavior is nondeterministic if binary_op is not associative.

Overloads (2,4) are executed according to policy. This overload participates in overload resolution only if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

binary_op shall not invalidate iterators (including the end iterators) or subranges, nor modify elements in the ranges [first, last) or [d_first, d_first + (last - first)). Otherwise, the behavior is undefined.

Contents

Parameters

first, last - the range of elements to sum
d_first - the beginning of the destination range; may be equal to first
policy - the execution policy to use. See execution policy for details.
init - the initial value
binary_op - binary FunctionObject that will be applied in to the result of dereferencing the input iterators, the results of other binary_op, and init.
Type requirements
-
InputIt must meet the requirements of LegacyInputIterator.
-
OutputIt must meet the requirements of LegacyOutputIterator.
-
ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
-
T must meet the requirements of MoveConstructible. and binary_op(init, *first), binary_op(init, init), and binary_op(*first, *first) must be convertible to T

Return value

Iterator to the element past the last element written.

Complexity

O(last - first) applications of the binary operation

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Example

This section is incomplete
Reason: no example

See also

 computes the differences between adjacent elements in a range
(function template) [edit]
sums up or folds a range of elements
(function template) [edit]
computes the partial sum of a range of elements
(function template) [edit]
(C++17)
 applies an invocable, then calculates exclusive scan
(function template) [edit]
(C++17)
 similar to std::partial_sum, includes the ith input element in the ith sum
(function template) [edit]
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