std::transform_exclusive_scan (3)  Linux Manuals
std::transform_exclusive_scan: std::transform_exclusive_scan
NAME
std::transform_exclusive_scan  std::transform_exclusive_scan
Synopsis
Defined in header <numeric>
template< class InputIt, class OutputIt, class T,
class BinaryOperation, class UnaryOperation> (1) (since C++17)
OutputIt transform_exclusive_scan( InputIt first, InputIt last, OutputIt d_first, T init,
BinaryOperation binary_op, UnaryOperation unary_op);
template< class ExecutionPolicy,
class ForwardIt1, class ForwardIt2,
class T, class BinaryOperation, class UnaryOperation >
ForwardIt2 transform_exclusive_scan( ExecutionPolicy&& policy, (2) (since C++17)
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 d_first, T init,
BinaryOperation binary_op, UnaryOperation unary_op );
Transforms each element in the range [first, last) with unary_op, then computes an exclusive prefix sum operation using binary_op over the resulting range, with init as the initial value, and writes the results to the range beginning at d_first. "exclusive" means that the ith input element is not included in the ith sum.
Formally, assigns through each iterator i in [d_first, d_first + (last  first)) the value of the generalized noncommutative sum of init, unary_op(*j)... for every j in [first, first + (i  d_first)) over binary_op,
where generalized noncommutative sum GNSUM(op, a
1, ..., a
N) is defined as follows:
* if N=1, a
* if N > 1, op(GNSUM(op, a
In other words, the summation operations may be performed in arbitrary order, and the behavior is nondeterministic if binary_op is not associative.
Overload (2) is executed according to policy, and does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.
unary_op and 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.
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
unary_op  unary FunctionObject that will be applied to each element of the input range. The return type must be acceptable as input to binary_op.
binary_op  binary FunctionObject that will be applied in to the result of unary_op, 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. All of binary_op(init, unary_op(*first)), binary_op(init, init), and binary_op(unary_op(*first), unary_op(*first)) must be convertible to T.
Return value
Iterator to the element past the last element written.
Complexity
O(last  first) applications of each of binary_op and unary_op.
Exceptions
The overload with a template parameter named ExecutionPolicy reports 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 implementationdefined.
* If the algorithm fails to allocate memory, std::bad_alloc is thrown.
Notes
unary_op is not applied to init.
Example
// Run this code
Output:
See also
partial_sum (function template)
exclusive_scan similar to std::partial_sum, excludes the ith input element from the ith sum
(C++17)
transform_inclusive_scan applies a functor, then calculates inclusive scan
(C++17)