13

solutions/13/README.md

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+# 13
+
+The second part one was really interesting. While my solution is correct, it takes way to much time in the data set.
+I started by checking what is the biggest ID number and check each location.
+
+<details>
+  <summary>Solutions</summary>
+  <ol>
+    <li>156</li>
+    <li>404517869995362</li>
+  </ol>
+</details>

solutions/13/python/main.py

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+from os.path import join, dirname
+from typing import List, Tuple
+from math import ceil, floor
+
+
+class Station:
+
+    def __init__(self, txt: str) -> None:
+        arrival, busses = txt.strip().split('\n')
+        self.arrival = int(arrival)
+        self.busses = [
+            int(bus)
+            for bus in busses.replace('x', '0').split(',')
+        ]
+
+    @staticmethod
+    def get_next_for_id(id: int, arrival: int) -> int:
+        return id * ceil(arrival / id)
+
+    def find_next(self) -> Tuple[int, int]:
+        arrivals: List[Tuple[int, int]] = []
+        for bus in self.busses:
+            if bus == 0:
+                continue
+            arrivals.append((bus, self.get_next_for_id(bus, self.arrival)))
+        return min(arrivals, key=lambda x: x[1])
+
+    def get_flag(self) -> int:
+        id, arrives = self.find_next()
+        return id * (arrives - self.arrival)
+
+    def contest(self, offset: int = 1) -> int:
+        # Prepare
+        highest = max(self.busses)
+        highest_i = self.busses.index(highest)
+        others = [
+            (bus, i - highest_i)
+            for i, bus in enumerate(self.busses)
+            if bus != 0 and i != highest_i
+        ]
+        others.sort(key=lambda x: x[0], reverse=True)
+
+        # Compute
+        i: int = max(1, floor(offset / highest))
+        while True:
+            x = highest * i
+            error = False
+            for bus, diff in others:
+                dx = x + diff
+                if dx != self.get_next_for_id(bus, dx):
+                    error = True
+                    break
+            if not error:
+                return x - highest_i
+            i += 1
+
+
+data = join(dirname(__file__), '../data.txt')
+with open(data) as f:
+
+    # Some "testing"
+    all = {
+        '17,x,13,19': 3417,
+        '67,7,59,61': 754018,
+        '67,x,7,59,61': 779210,
+        '67,7,x,59,61': 1261476,
+        '1789,37,47,1889': 1202161486,
+    }
+    for busses, expected in all.items():
+        station = Station('69\n' + busses)
+        print(expected, expected == station.contest())
+
+    txt = f.read()
+    station = Station(txt)
+    print(station.get_flag())
+    print(station.contest(offset=10**14))