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adjacent_difference

Category: algorithms Component type: function

Prototype

Adjacent_difference is an overloaded name; there are actually two adjacent_difference functions.
template <class InputIterator, class OutputIterator>
OutputIterator adjacent_difference(InputIterator first, InputIterator last, 
                                   OutputIterator result);

template <class InputIterator, class OutputIterator, class BinaryFunction>
OutputIterator adjacent_difference(InputIterator first, InputIterator last,
                                   OutputIterator result,
                                   BinaryFunction binary_op);

Description

Adjacent_difference calculates the differences of adjacent elements in the range [first, last). This is, *first is assigned to *result [1], and, for each iterator i in the range [first + 1, last), the difference of *i and *(i - 1) is assigned to *(result + (i - first)). [2]

The first version of adjacent_difference uses operator- to calculate differences, and the second version uses a user-supplied binary function. In the first version, for each iterator i in the range [first + 1, last), *i - *(i - 1) is assigned to *(result + (i - first)). In the second version, the value that is assigned to *(result + 1) is instead binary_op(*i, *(i - 1)).

Definition

Defined in the standard header numeric, and in the nonstandard backward-compatibility header algo.h.

Requirements on types

For the first version: For the second version:

Preconditions

Complexity

Linear. Zero applications of the binary operation if [first, last) is an empty range, otherwise exactly (last - first) - 1 applications.

Example

int main()
{
  int A[] = {1, 4, 9, 16, 25, 36, 49, 64, 81, 100};
  const int N = sizeof(A) / sizeof(int);
  int B[N];

  cout << "A[]:         ";
  copy(A, A + N, ostream_iterator<int>(cout, " "));
  cout << endl;
  
  adjacent_difference(A, A + N, B);
  cout << "Differences: ";
  copy(B, B + N, ostream_iterator<int>(cout, " "));
  cout << endl;

  cout << "Reconstruct: ";
  partial_sum(B, B + N, ostream_iterator<int>(cout, " "));
  cout << endl;
}

Notes

[1] The reason it is useful to store the value of the first element, as well as simply storing the differences, is that this provides enough information to reconstruct the input range. In particular, if addition and subtraction have the usual arithmetic definitions, then adjacent_difference and partial_sum are inverses of each other.

[2] Note that result is permitted to be the same iterator as first. This is useful for computing differences "in place".

See also

partial_sum, accumulate, inner_product, count


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