aoc-2021-rust

Advent of Code 2021 Solutions in Rust
git clone https://git.sinitax.com/sinitax/aoc-2021-rust
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part1 (2801B)

      1--- Day 14: Extended Polymerization ---
      2
      3The incredible pressures at this depth are starting to put a strain on your submarine. The submarine
      4has polymerization equipment that would produce suitable materials to reinforce the submarine, and
      5the nearby volcanically-active caves should even have the necessary input elements in sufficient
      6quantities.
      7
      8The submarine manual contains instructions for finding the optimal polymer formula; specifically, it
      9offers a polymer template and a list of pair insertion rules (your puzzle input). You just need to
     10work out what polymer would result after repeating the pair insertion process a few times.
     11
     12For example:
     13
     14NNCB
     15
     16CH -> B
     17HH -> N
     18CB -> H
     19NH -> C
     20HB -> C
     21HC -> B
     22HN -> C
     23NN -> C
     24BH -> H
     25NC -> B
     26NB -> B
     27BN -> B
     28BB -> N
     29BC -> B
     30CC -> N
     31CN -> C
     32
     33The first line is the polymer template - this is the starting point of the process.
     34
     35The following section defines the pair insertion rules. A rule like AB -> C means that when elements
     36A and B are immediately adjacent, element C should be inserted between them. These insertions all
     37happen simultaneously.
     38
     39So, starting with the polymer template NNCB, the first step simultaneously considers all three
     40pairs:
     41
     42
     43 - The first pair (NN) matches the rule NN -> C, so element C is inserted between the first N and
     44the second N.
     45
     46 - The second pair (NC) matches the rule NC -> B, so element B is inserted between the N and the C.
     47
     48 - The third pair (CB) matches the rule CB -> H, so element H is inserted between the C and the B.
     49
     50
     51Note that these pairs overlap: the second element of one pair is the first element of the next pair.
     52Also, because all pairs are considered simultaneously, inserted elements are not considered to be
     53part of a pair until the next step.
     54
     55After the first step of this process, the polymer becomes
     56NCNBCHB.
     57
     58Here are the results of a few steps using the above rules:
     59
     60Template:     NNCB
     61After step 1: NCNBCHB
     62After step 2: NBCCNBBBCBHCB
     63After step 3: NBBBCNCCNBBNBNBBCHBHHBCHB
     64After step 4: NBBNBNBBCCNBCNCCNBBNBBNBBBNBBNBBCBHCBHHNHCBBCBHCB
     65
     66This polymer grows quickly. After step 5, it has length 97; After step 10, it has length 3073. After
     67step 10, B occurs 1749 times, C occurs 298 times, H occurs 161 times, and N occurs 865 times; taking
     68the quantity of the most common element (B, 1749) and subtracting the quantity of the least common
     69element (H, 161) produces 1749 - 161 = 1588.
     70
     71Apply 10 steps of pair insertion to the polymer template and find the most and least common elements
     72in the result. What do you get if you take the quantity of the most common element and subtract the
     73quantity of the least common element?
     74
     75