Add task desctiption for each day

day-14/README.md

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+# Day 14: Extended Polymerization
+
+[https://adventofcode.com/2021/day/14](https://adventofcode.com/2021/day/14)
+
+## Description
+
+### Part One
+
+The incredible pressures at this depth are starting to put a strain on your submarine. The submarine has [polymerization](https://en.wikipedia.org/wiki/Polymerization) equipment that would produce suitable materials to reinforce the submarine, and the nearby volcanically-active caves should even have the necessary input elements in sufficient quantities.
+
+The submarine manual contains <span title="HO
+
+HO -> OH">instructions</span> for finding the optimal polymer formula; specifically, it offers a _polymer template_ and a list of _pair insertion_ rules (your puzzle input). You just need to work out what polymer would result after repeating the pair insertion process a few times.
+
+For example:
+
+    NNCB
+    
+    CH -> B
+    HH -> N
+    CB -> H
+    NH -> C
+    HB -> C
+    HC -> B
+    HN -> C
+    NN -> C
+    BH -> H
+    NC -> B
+    NB -> B
+    BN -> B
+    BB -> N
+    BC -> B
+    CC -> N
+    CN -> C
+    
+
+The first line is the _polymer template_ - this is the starting point of the process.
+
+The following section defines the _pair insertion_ rules. A rule like `AB -> C` means that when elements `A` and `B` are immediately adjacent, element `C` should be inserted between them. These insertions all happen simultaneously.
+
+So, starting with the polymer template `NNCB`, the first step simultaneously considers all three pairs:
+
+*   The first pair (`NN`) matches the rule `NN -> C`, so element _`C`_ is inserted between the first `N` and the second `N`.
+*   The second pair (`NC`) matches the rule `NC -> B`, so element _`B`_ is inserted between the `N` and the `C`.
+*   The third pair (`CB`) matches the rule `CB -> H`, so element _`H`_ is inserted between the `C` and the `B`.
+
+Note that these pairs overlap: the second element of one pair is the first element of the next pair. Also, because all pairs are considered simultaneously, inserted elements are not considered to be part of a pair until the next step.
+
+After the first step of this process, the polymer becomes `NCNBCHB`.
+
+Here are the results of a few steps using the above rules:
+
+    Template:     NNCB
+    After step 1: NCNBCHB
+    After step 2: NBCCNBBBCBHCB
+    After step 3: NBBBCNCCNBBNBNBBCHBHHBCHB
+    After step 4: NBBNBNBBCCNBCNCCNBBNBBNBBBNBBNBBCBHCBHHNHCBBCBHCB
+    
+
+This polymer grows quickly. After step 5, it has length 97; After step 10, it has length 3073. After step 10, `B` occurs 1749 times, `C` occurs 298 times, `H` occurs 161 times, and `N` occurs 865 times; taking the quantity of the most common element (`B`, 1749) and subtracting the quantity of the least common element (`H`, 161) produces `1749 - 161 = 1588`.
+
+Apply 10 steps of pair insertion to the polymer template and find the most and least common elements in the result. _What do you get if you take the quantity of the most common element and subtract the quantity of the least common element?_
+
+### Part Two
+
+The resulting polymer isn't nearly strong enough to reinforce the submarine. You'll need to run more steps of the pair insertion process; a total of _40 steps_ should do it.
+
+In the above example, the most common element is `B` (occurring `2192039569602` times) and the least common element is `H` (occurring `3849876073` times); subtracting these produces _`2188189693529`_.
+
+Apply _40_ steps of pair insertion to the polymer template and find the most and least common elements in the result. _What do you get if you take the quantity of the most common element and subtract the quantity of the least common element?_