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  1. import sys, math
  2.  
  3. def lower_hull(pts):
  4.     pts = sorted(pts)  # sort by x, then y
  5.     hull = []
  6.     for p in pts:
  7.         while len(hull) >= 2:
  8.             x1, y1 = hull[-2]
  9.             x2, y2 = hull[-1]
  10.             x3, y3 = p
  11.             cross = (x2 - x1) * (y3 - y1) - (y2 - y1) * (x3 - x1)
  12.             if cross <= 0:  # not a left turn → pop
  13.                 hull.pop()
  14.             else:
  15.                 break
  16.         hull.append(p)
  17.     return hull
  18.  
  19. def main():
  20.     data = [s for s in sys.stdin.read().strip().split()]
  21.     if not data:
  22.         return
  23.     it = iter(data)
  24.     n = int(next(it))
  25.     pts = [(int(next(it)), int(next(it))) for _ in range(n)]
  26.  
  27.     hull = lower_hull(pts)
  28.  
  29.     perim = 0.0
  30.     for i in range(len(hull) - 1):
  31.         x1, y1 = hull[i]
  32.         x2, y2 = hull[i + 1]
  33.         perim += math.hypot(x2 - x1, y2 - y1)
  34.  
  35.     # round to nearest integer, .5 rounds up
  36.     ans = int(math.floor(perim + 0.5))
  37.     print(ans)
  38.  
  39. if __name__ == "__main__":
  40.     main()
  41.  
Success #stdin #stdout 0.09s 14156KB
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stdout 
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https://ideone.com/gMUzkN
language:
Python 3 (python  3.12)
created:
17 days ago
visibility:
public

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