Solution to the 5th problem

Problem A

The answer for part A is pretty straightforward, as it simply requires that we execute each movement, the amount of times defined in the amount field of each move. Each stack work as a stack data structure, therefore the last element added is the first one to be removed. This logic is executed until there are no movements left.

» cargo build -p aoc-22 --release && hyperfine ./target/release/aoc-22 -N --warmup 5
Benchmark 1: ./target/release/aoc-22
Time (mean ± σ):       4.8 ms ±   1.7 ms    [User: 1.1 ms, System: 0.9 ms]
Range (min … max):     3.1 ms …  18.5 ms    511 runs

Problem B

Part B is really similar to the part A, yet in this case when we remove elements from a stack, we cannot do it using a FIFO approach, but rather we need to move the amount of items at the same time, keeping their order. The most simple solution is to slice method from the array, but starting from the end, and taking amount elements. This way, we keep the order of the elements without needing to reverse them.

If you check the solver code, you'll see that we are using splice instead, so we can mutate the array from which we are extracting the elements, at the same time we are taking them. If we were to use slice, we would then have to manually mutate the array, removing the extracted elements.

» cargo build -p aoc-23 --release && hyperfine ./target/release/aoc-23 -N --warmup 5
Benchmark 1: ./target/release/aoc-22
Time (mean ± σ):       5.8 ms ±   4.0 ms    [User: 1.2 ms, System: 1.0 ms]
Range (min … max):     3.2 ms …  55.5 ms    421 runs