Problem 40. Reverse Run-Length Encoder

Given a "counting sequence" vector x, construct the original sequence y.

A counting sequence is formed by "counting" the entries in a given sequence. This is sometimes called run-length encoding.

For example, the sequence

 x = 2, 5, 1, 2, 4, 1, 1, 3

can be read as

 Two 5's, one 2, four 1's, one 3

which translates to

 y = 5, 5, 2, 1, 1, 1, 1, 3

So y is the reconstructed vector that corresponds to the counting sequence x.

For this problem, all elements in the sequences x and y will be in the range from 1 to 9.