Category: algorithms | Component type: function |
template <class InputIterator1, class InputIterator2, class OutputIterator> OutputIterator set_symmetric_difference(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result); template <class InputIterator1, class InputIterator2, class OutputIterator, class StrictWeakOrdering> OutputIterator set_symmetric_difference(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result, StrictWeakOrdering comp);
In the simplest case, set_symmetric_difference performs a set theoretic calculation: it constructs the union of the two sets A - B and B - A, where A and B are the two input ranges. That is, the output range contains a copy of every element that is contained in [first1, last1) but not [first2, last2), and a copy of every element that is contained in [first2, last2) but not [first1, last1). The general case is more complicated, because the input ranges may contain duplicate elements. The generalization is that if a value appears m times in [first1, last1) and n times in [first2, last2) (where m or n may be zero), then it appears |m-n| times in the output range. [1] Set_symmetric_difference is stable, meaning that the relative order of elements within each input range is preserved.
The two versions of set_symmetric_difference differ in how they define whether one element is less than another. The first version compares objects using operator<, and the second compares objects using a function object comp.
inline bool lt_nocase(char c1, char c2) { return tolower(c1) < tolower(c2); } int main() { int A1[] = {1, 3, 5, 7, 9, 11}; int A2[] = {1, 1, 2, 3, 5, 8, 13}; char A3[] = {'a', 'b', 'b', 'B', 'B', 'f', 'g', 'h', 'H'}; char A4[] = {'A', 'B', 'B', 'C', 'D', 'F', 'F', 'H' }; const int N1 = sizeof(A1) / sizeof(int); const int N2 = sizeof(A2) / sizeof(int); const int N3 = sizeof(A3); const int N4 = sizeof(A4); cout << "Symmetric difference of A1 and A2: "; set_symmetric_difference(A1, A1 + N1, A2, A2 + N2, ostream_iterator<int>(cout, " ")); cout << endl << "Symmetric difference of A3 and A4: "; set_symmetric_difference(A3, A3 + N3, A4, A4 + N4, ostream_iterator<char>(cout, " "), lt_nocase); cout << endl; }
The output is
Symmetric difference of A1 and A2: 1 2 7 8 9 11 13 Symmetric difference of A3 and A4: B B C D F g H
[1] Even this is not a completely precise description, because the ordering by which the input ranges are sorted is permitted to be a strict weak ordering that is not a total ordering: there might be values x and y that are equivalent (that is, neither x < y nor y < x) but not equal. See the LessThan Comparable requirements for a more complete discussion. The output range consists of those elements from [first1, last1) for which equivalent elements do not exist in [first2, last2), and those elements from [first2, last2) for which equivalent elements do not exist in [first1, last1). Specifically, suppose that the range [first1, last1) contains m elements that are equivalent to each other and the range [first2, last2) contains n elements from that equivalence class (where either m or n may be zero). If m > n then the output range contains the last m - n of these elements elements from [first1, last1), and if m < n then the output range contains the last n - m of these elements elements from [first2, last2).