题解 | 特殊城市
特殊城市
https://www.nowcoder.com/practice/46f68af83db74b709a788dedb656c5f9
import sys
from collections import defaultdict
n, d, t = int(sys.stdin.readline()), defaultdict(int), 0
for _ in range(n):
s, c = sys.stdin.readline().split()
d[(s[:2],c)] += 1
for (a,b) in d.keys():
if a<b and (b,a) in d.keys():
t+=d[(a,b)]*d[(b,a)]
print(t)