58 lines
1.8 KiB
Python
58 lines
1.8 KiB
Python
def parse(input):
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ranges = []
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ids = []
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with open(input) as f:
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for line in f:
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line = line.strip()
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if line == "":
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break
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lo, _, hi = line.partition("-")
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ranges.append((int(lo), int(hi)))
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for line in f:
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ids.append(int(line.strip()))
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return ranges, ids
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def solve(input):
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# Part 1: count the number of given ids which are within one of the ranges
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ranges, ids = parse(input)
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t = 0
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for x in ids:
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for lo,hi in ranges:
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if lo <= x <= hi:
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t += 1
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break
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print(t)
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# Part 2: count the number of possible ids which are within one of the ranges --
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# in other words, the size of the union of all the ranges.
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#
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# We start by flattening the ranges so that they don't overlap with each other
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flattened = []
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queue = list(ranges)
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while queue:
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lo, hi = queue.pop()
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found = False
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for i,(x,y) in enumerate(flattened):
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if not (hi < x or y < lo):
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found = True
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break
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if found:
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#print("collapsing ({:,} {:,}) and ({:,} {:,}) -> ({:,} {:,})".format(x,y,lo,hi,min(x,lo),max(y,hi)))
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# if x <= lo <= hi < y then the range is unchanged and we don't need to update flattened[i].
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# otherwise we need to add the new range to the queue to see if it can be merged with any other entries.
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if lo < x or hi > y:
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del flattened[i]
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queue.append((min(x,lo), max(y,hi)))
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else:
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flattened.append((lo,hi))
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# Then we sum up their sizes. Ranges are inclusive, so +1.
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t = 0
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for x,y in flattened:
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t += y-x + 1
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print(t)
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solve("sample")
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solve("input")
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