2016: d20: ex2: add solution

2016/d20/ex2/ex2.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python
+
+import sys
+from typing import NamedTuple
+
+
+class Interval(NamedTuple):
+    start: int
+    end: int
+
+    @classmethod
+    def from_str(cls, input: str) -> "Interval":
+        start, end = input.split("-")
+        return cls(int(start), int(end))
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> list[Interval]:
+        return [Interval.from_str(line) for line in input.splitlines()]
+
+    def merge_overlaps(intervals: list[Interval]) -> list[Interval]:
+        # Sort intervals by start, then merge overlapping ones
+        intervals = sorted(intervals)
+        res = [intervals[0]]
+        for interval in intervals[1:]:
+            # `+ 1` to merge [0, 2] and [2, 5]
+            if interval.start <= (res[-1].end + 1):
+                res[-1] = Interval(res[-1].start, max(interval.end, res[-1].end))
+            else:
+                res.append(interval)
+        return res
+
+    intervals = parse(input)
+    intervals = merge_overlaps(intervals)
+    return (1 << 32) - sum((end - start + 1) for start, end in intervals)
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()