08

2021/08/README.md

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+# 08
+
+This was super fun and another episode of "I should have gotten my paper out sooner".
+
+As soon as I realized you can take the statistical approach to decode the numbers.
+
+1. Count all characters
+
+This will reveal the mapping for the letters `b`, `e` and `f`, as they appear a unique amount of times.
+
+2. `a` & `c`
+
+Both appear 8 times. We find `a` by looking at the `1` and `7`. If we identify `1` (cf) and `7` (afc) we can simply calculate what `a` is by difference. With `a` identified `c` is also determined.
+
+3. `d` & `g`
+
+Both appear 7 times. We take the similar approach as in 2.
+
+This ensures a linear time execution.
+
+<details>
+  <summary>Solutions</summary>
+  <ol>
+    <li>449</li>
+    <li>968175</li>
+  </ol>
+</details>

2021/08/python/main.py

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+#!/usr/bin/env python
+
+from os.path import join, dirname
+from typing import Dict, List, Set
+
+# Day 08
+
+# Common
+
+
+def read_input(filename):
+    data = join(dirname(__file__), '..', filename)
+    with open(data) as f:
+        return f.read().strip()
+
+
+test = read_input('test.txt')
+data = read_input('input.txt')
+
+
+class Utils:
+    @staticmethod
+    def count_chars(items: List[str]) -> Dict[str, int]:
+        count = {}
+        for item in items:
+            for char in item:
+                if char not in count:
+                    count[char] = 0
+                count[char] += 1
+        return count
+
+    @staticmethod
+    def group_by_length(items: List[str]) -> Dict[int, List[str]]:
+        groups = {}
+        for item in items:
+            l = len(item)
+            if l not in groups:
+                groups[l] = []
+            groups[l].append(item)
+        return groups
+
+
+class SevenSegment:
+    mappings = {
+        0: 'abcefg',
+        1: 'cf',
+        2: 'acdeg',
+        3: 'acdfg',
+        4: 'bcdf',
+        5: 'abdfg',
+        6: 'abdefg',
+        7: 'acf',
+        8: 'abcdefg',
+        9: 'abcdfg'
+    }
+    reverse = {v: k for k, v in mappings.items()}
+    count: Dict[str, int] = Utils.count_chars(mappings.values())
+
+    @staticmethod
+    def encode(number: int) -> str:
+        return SevenSegment.mappings[number]
+
+    @staticmethod
+    def decode(segment: str) -> int:
+        normalized: str = ''.join(sorted(list(segment)))
+        return SevenSegment.reverse[normalized]
+
+
+class Reading:
+    def __init__(self, input: List[str], output: List[str]) -> None:
+        self.input = input
+        self.output = output
+        self.transformations: Dict[str, str] = {}
+
+    def translate(self, segment: str) -> str:
+        return ''.join([self.transformations[char] for char in segment])
+
+    def analyse(self):
+        count = Utils.count_chars(self.input)
+        by_length = Utils.group_by_length(self.input)
+
+        # Find a & c
+        # 1 and 7 have the same chars with the only difference of the 'a'
+        one = set(by_length[2][0])
+        seven = set(by_length[3][0])
+        a = seven.difference(one).pop()
+
+        dg: Set[str] = set()
+
+        # Find b, e & f by statistical analysis
+        for k, v in count.items():
+            if v == 6:
+                b = k
+                self.transformations[k] = 'b'
+            elif v == 4:
+                self.transformations[k] = 'e'
+            elif v == 9:
+                self.transformations[k] = 'f'
+            elif v == 8:
+                if k == a:
+                    self.transformations[k] = 'a'
+                else:
+                    self.transformations[k] = 'c'
+            elif v == 7:
+                dg.add(k)
+
+        # Find d by looking at the 1 and 4
+        # We already know b so, we subtract cf (1) from bcdf (4) and are left with bd.
+        four = set(by_length[4][0])
+        bd = four.difference(one)
+        d = bd.difference(b).pop()
+        self.transformations[d] = 'd'
+        g = dg.difference(d).pop()
+        self.transformations[g] = 'g'
+
+    def read(self) -> List[int]:
+        return [SevenSegment.decode(self.translate(segment)) for segment in self.output]
+
+    @staticmethod
+    def parse(data: str):
+        input, output = data.split('|')
+        i = input.strip().split(' ')
+        o = output.strip().split(' ')
+        return Reading(i, o)
+
+
+class Log:
+    def __init__(self, readings: List[Reading]) -> None:
+        self.readings = readings
+
+    def flag(self, alt=False):
+        count = 0
+        for reading in self.readings:
+            reading.analyse()
+            numbers = reading.read()
+            if alt:
+                count += int(''.join([str(n) for n in numbers]))
+            else:
+                for number in numbers:
+                    if number == 1 or number == 4 or number == 7 or number == 8:
+                        count += 1
+        return count
+
+    @staticmethod
+    def parse(data: str):
+        return Log([Reading.parse(line) for line in data.split('\n')])
+
+
+# 1
+print('1.')
+
+log = Log.parse(test)
+result = log.flag()
+print(f"Test: {result}")
+
+log = Log.parse(data)
+result = log.flag()
+print(f"Result: {result}")
+
+# 2
+print('\n2.')
+
+log = Log.parse(test)
+result = log.flag(True)
+print(f"Test: {result}")
+
+log = Log.parse(data)
+result = log.flag(True)
+print(f"Result: {result}")