This program illustrates the use of the STL sort() algorithm (extended version)
to sort a vector of integers, when a first integer comes before a second if and
only if the first has a smaller digit sum than the second.
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Here are the original contents of the vector:
17 12 14 19 23 15 61 20 81 11
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And here the sorted contents of the vector:
20 11 12 14 23 15 61 17 81 19
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