We are given a list
nums of integers representing a list compressed with run-length encoding.
Consider each adjacent pair of elements
[freq, val] = [nums[2*i], nums[2*i+1]] (with
i >= 0). For each such pair, there are
freq elements with value
val concatenated in a sublist. Concatenate all the sublists from left to right to generate the decompressed list.
Return the decompressed list.