This program illustrates the use of the STL partial_sort_copy() algorithm
(extended version) to order a range of values from a vector of integers of
size 12 into the order determined by increasing digit sum, and copy as many
of them as will fit into a range within a second vector of integers. The
contents of the initial vector are unchanged by this action.
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Here are the initial contents of vector v1:
92 21 53 84 46 13 41 76 45 61 11 15
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Here are the initial contents of vector v2:
100 200 300 400 500
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Now we make the following call:
p = partial_sort_copy(v1.begin(), v1.end(),
    v2.begin(), v2.begin()+3, hasSmallerDigitSum);
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After that call, here are the contents of v1:
92 21 53 84 46 13 41 76 45 61 11 15
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And here are the contents of v2:
11 21 13 400 500
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The iterator p returned by the algorithm points to the value 400.
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Next we make the following call:
p = partial_sort_copy(v1.begin()+2, v1.end()-2,
    v2.begin(), v2.end(), hasSmallerDigitSum);
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After that call, here are the contents of v1:
92 21 53 84 46 13 41 76 45 61 11 15
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And here are the contents of v2:
13 41 61 53 45
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The iterator p returned by the algorithm points to
the end of the ouput container.
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