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+#!/usr/bin/python3
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+
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+"""Solution for day 20 of Advent of Code 2016.
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+
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+This solution first compresses the blacklist by merging overlapping sections, using functools.reduce and the merge
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+function below. For example, [(0, 100), (50, 150)] becomes (0, 150). The blacklist is then inverted to become a
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+whitelist, which gives both answers pretty easily.
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+"""
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+
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+import functools
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+
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+def merge(x, y):
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+ if y[0] <= x[-1][1] + 1:
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+ # This entry overlaps with the last one, combine them
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+ x[-1] = (x[-1][0], max(y[1], x[-1][1]))
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+ else:
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+ # New, non-overlapping entry, just append it to our list
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+ x.append(y)
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+ return x
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+
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+with open('data/20.txt', 'r') as file:
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+ ranges = sorted(list(map(lambda x: tuple(map(int, x.strip().split('-'))), file.readlines())))
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+ blacklist = functools.reduce(merge, ranges[1:], [ranges[0]])
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+
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+ whitelist = []
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+ last = 0
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+ for pair in blacklist:
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+ if pair[0] > last:
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+ whitelist.append((last, pair[0] - 1))
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+ last = pair[1] + 1
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+ if last < 4294967295:
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+ whitelist.append((last, 4294967295))
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+
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+ print("Part 1: %s" % whitelist[0][0])
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+ print("Part 2: %s" % sum(map(lambda p: 1 + p[1] - p[0], whitelist)))
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