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# AOJ 1127 - Building a Space Station

Atcoderのなかに答えなかったので、自分用のメモ。

sample.py
```import math
import heapq
while True:
n = int(input())
if n==0: break
if n==1: print(0);exit()
edges = [[] for _ in range(n)]
coordinates = []
for _ in range(n):
x,y,z,r = map(float,input().split())
coordinates.append((x,y,z,r))
for i in range(n):
for j in range(i+1,n):
dist = math.sqrt((coordinates[i][0]-coordinates[j][0])**2 + (coordinates[i][1]-coordinates[j][1])**2+(coordinates[i][2]-coordinates[j][2])**2)
if coordinates[i][3] + coordinates[j][3]>=dist:
dist = 0
else:
dist -=coordinates[i][3] + coordinates[j][3]
edges[i].append((dist,j))
edges[j].append((dist,i))
seen = [False]*n
hq = []
res = 0
for e in edges[0]:
heapq.heappush(hq,e)
seen[0] = True
while len(hq):
minedge = heapq.heappop(hq)
if seen[minedge[1]]:
continue
seen[minedge[1]] = True
v = minedge[1]
for e in edges[v]:
heapq.heappush(hq,e)
res += minedge[0]
print(f"{res:.3f}")
```

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