Day 13

Author: Chris Poch

13-1.txt

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+939
+7,13,x,x,59,x,31,19

13-2.txt

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+2
+17,x,13,19

13-3.txt

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+3
+67,7,59,61

13-4.txt

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+4
+67,x,7,59,61

13-5.txt

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+5
+67,7,x,59,61

13-6.txt

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+6
+1789,37,47,1889

13.py

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+import os
+import sys
+
+debug = False
+fileName = ""
+try:
+    fileName = sys.argv[1]
+    if len(fileName) < 1:
+        fileName = "13.txt"
+except:
+    fileName = "13.txt"
+print(fileName)
+
+with open(fileName) as file:
+    time = int(file.readline())
+    note = file.readline()
+    note2 = note.replace(",x","")
+    buses = note2.split(",")
+    for i in range(len(buses)):
+        buses[i] = int(buses[i])
+    leaves = []
+
+    for i in range(len(buses)):
+        leaves.append(time + buses[i] - (time % buses[i]))
+    
+    min = leaves[0]
+    mini = 0
+    for i in range(len(leaves)):
+        if leaves[i] < min:
+            min = leaves[i]
+            mini = i
+    wait = leaves[mini] - time
+    print(buses[mini], wait, buses[mini] * wait)
+
+    #part 2
+    print("Part 2")
+    buses = note.split(",")
+    #print(buses)
+    for i in range(len(buses)):
+        if buses[i] == "x":
+            buses[i] = 0
+        else:
+            #print(buses[i])
+            buses[i] = int(buses[i])
+    leaves = []
+    for bus in buses:
+        leaves.append(0)
+
+    time = 0
+    step = 1
+    #influenced by https://gist.github.com/joshbduncan/65f810fe821c7a3ea81a1f5a444ea81e
+    """Since you must find departure times for each bus based off of the previous bus schedule (which is based on the previous bus and so on...), all following buses must depart at a multiple of all previous buses departures since they have to stay in the order provided.
+
+Step Progression
+1 * 7 = 7
+7 * 13 = 91
+91 * 59 = 5369
+5369 * 31 = 166439
+
+Then you just need to add the cumulative time (t) and the minute offset for each bus in the list to get the final answer."""
+    p2 = [(int(i), j) for j, i in enumerate(buses) if i != 0]
+    for bus, offset in p2:
+        while (time + offset) % bus != 0:
+            time += step
+        step *= bus
+
+    print(time)
+

13.txt

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+1000655
+17,x,x,x,x,x,x,x,x,x,x,37,x,x,x,x,x,571,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,13,x,x,x,x,23,x,x,x,x,x,29,x,401,x,x,x,x,x,x,x,x,x,41,x,x,x,x,x,x,x,x,19