Fix various typos in all walkthroughs

Author: mebeim

2020/README.md

@@ -3382,7 +3382,7 @@ def is_valid(ticket):
 ```
 
 Sweet. Now we just need to filter out invalid tickets and only work with valid
-ones. Perfect use case for the [`filter()`][py-builtin-filter] buil-in. Then,
+ones. Perfect use case for the [`filter()`][py-builtin-filter] built-in. Then,
 for each valid ticket, for each field we want to check if any of the ticket
 values violate that particular field's validity requirements. If so, we'll
 remove the index of that value as a possible index for the field.
@@ -3713,7 +3713,7 @@ dimensions.
 Oh no! The code we wrote works with 3 dimensions, do we need to rewrite
 everything? Well, not quite, the only function that would need to be updated is
 `neighbors()`, since it takes exactly 3 arguments. We can make a small change to
-generalize it to work with any dimension.
+generalize it to work with any number of dimensions.
 
 To generate neighbor coordinates, we would need to take an additional parameter
 `w` for the fourth dimension, but since we want this to be general, taking a

2021/README.md

@@ -5010,7 +5010,7 @@ different points to keep track of... a little bit too many to fit in memory
 As usual, there are different ways to solve today's problem:
 
 1. The most optimal solution in terms of time complexity is probably using
-   [segment trees][wiki-segment-tree], however it also the most complex one to
+   [segment trees][wiki-segment-tree], however it's also the most complex one to
    actually implement. There are other solutions that work just fine given the
    number of commands in our input isn't that large.
 

2022/README.md

@@ -3714,8 +3714,8 @@ mutable, but we can use a `frezenset` (the immutable variant of a `set`).
 maxscore = defaultdict(int)
 
 for solution in solutions(distance, rates, good, 26):
-    k = frozenset(choice)
-    s = score(rates, choice)
+    k = frozenset(solution)
+    s = score(rates, solution)
 
     if s > maxscore[k]:
         maxscore[k] = s
@@ -4314,8 +4314,8 @@ def best_case_scenario(initial_amount, robots, t):
 We can now use it to perform three optimizations of the same kind any time we
 visit a new state:
 
-1. If the amount of geodes achievable in the best-case scenario number is lower
-   than the current `best` we have, we can discard the state and any of its
+1. If the amount of geodes achievable in the best-case scenario is lower than
+   the current `best` we have, we can discard the state and any of its
    successors.
 2. If the amount of obsidian achievable in the best-case scenario is lower than
    the amount needed to build a geode robot, we know we'll never be able to
@@ -4428,7 +4428,7 @@ def search(blueprint):
                 q.append((..., []))
 
         # If we can also "wait" without building, pass along the list of robots
-        # we couldhave built, but decided to not build instead.
+        # we could whave built, but decided to not build instead.
         if (robs and obs < max_obs_needed) or (rclay and clay < max_clay_needed) or ore < max_ore_needed:
             q.append((..., can_build))
 
@@ -4752,7 +4752,9 @@ use [`isinstance()`][py-builtin-isinstance] to check whether `T[node]` is a
 it could also be passed as parameter.
 
 ```python
-def calc(value, list):
+def calc(node):
+    value = T[node]
+	if not isinstance(node, list):
         # This is a value node, just return the value.
         return value
 
@@ -4945,7 +4947,7 @@ rvalue = calc(r)
 if lvalue is None:
     answer = find_value(l, rvalue)
 else:
-    answer = find_value(r, rvalue)
+    answer = find_value(r, lvalue)
 ```
 
 Since `root` is `L == R`, we could also re-write it as `L - R`, knowing that the
@@ -5058,7 +5060,7 @@ for i in range(HEIGHT):
 Additionally, we will need an easy way to detect whether we are going out of
 bounds (and therefore need to wrap around). To avoid a bunch of annoying
 bound-checking `if` statements, we can simply add two rows of empty cells at the
-top and at the bottom of the grid, as weel as two columns of empty cells on the
+top and at the bottom of the grid, as well as two columns of empty cells on the
 left and the right. This also makes the actual grid start at `grid[1][x]` (where
 `x` is the column of the leftmost free cell in the top row) instead of
 `grid[0][x]`, which is nice since the coordinate system used in the problem

2023/README.md

@@ -71,8 +71,8 @@ for line in fin:
 
 We can simplify this with the help of the [`filter()`][py-builtin-filter]
 built-in function: just filter out any character that satisfies `str.isdigit()`.
-To only extrac the first such character from the iterator returned by `filter()`
-we can simply use [`next()`][py-builtin-next].
+To only extract the first such character from the iterator returned by
+`filter()` we can simply use [`next()`][py-builtin-next].
 
 ```python
 for line in fin:
@@ -179,7 +179,7 @@ for line in fin:
     total2 += next(filter(None, map(check_digit, (line[i:] for i in range(len(line) -1, -1, -1)))))
 ```
 
-First two starts of the year done. Welcome to Advent of Code 2024!
+First two stars of the year done. Welcome to Advent of Code 2023!
 
 
 Day 2 - Cube Conundrum
@@ -714,7 +714,7 @@ answer2     = sum(products)
 Or more concisely:
 
 ```python
-answer2 = map(prod, filter(lambda x: len(x) == 2, gears.values())))
+answer2 = sum(map(prod, filter(lambda x: len(x) == 2, gears.values()))))
 print('Part 2:', answer2)
 ```