||Component type: function
template <class BidirectionalIterator1, class BidirectionalIterator2>
BidirectionalIterator2 copy_backward(BidirectionalIterator1 first,
Copy_backward copies elements from the range [first, last) to the range
[result - (last - first), result) . That is, it performs the
assignments *(result - 1) = *(last - 1), *(result - 2) = *(last - 2),
and so on. Generally, for every integer n from 0 to last - first,
copy_backward performs the assignment *(result - n - 1) = *(last - n - 1).
Assignments are performed from the end of the input sequence to the
beginning, i.e. in order of increasing n. 
The return value is result - (last - first)
Defined in the standard header algorithm, and in the nonstandard
backward-compatibility header algo.h.
Requirements on types
BidirectionalIterator1 and BidirectionalIterator2 are
models of BidirectionalIterator.
BidirectionalIterator1's value type is convertible to
BidirectionalIterator2's value type.
[first, last) is a valid range.
result is not an iterator within the range [first, last).
There is enough space to hold all of the elements being copied.
More formally, the requirement is that
[result - (last - first), result) is a valid range.
Linear. Exactly last - first assignments are performed.
iota(V.begin(), V.end(), 1);
copy_backward(V.begin(), V.begin() + 10, V.begin() + 15);
Result is an iterator that points to the end of the output
range. This is highly unusual: in all other STL algorithms that
denote an output range by a single iterator, that iterator points to
the beginning of the range.
The order of assignments matters in the case where the input and
output ranges overlap: copy_backward may not be used if result is
in the range [first, last). That is, it may not be used if the
end of the output range overlaps with the input range, but it may be
used if the beginning of the output range overlaps with the input
range; copy has opposite restrictions.
If the two ranges are completely nonoverlapping, of course, then
either algorithm may be used.
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