Submission #5905421

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Source Code Expand

import heapq as h
orda = lambda x: ord(x)-ord("a")
ans = []
n =  int(input())
l = [set() for _ in range(26)]
r = [set() for _ in range(26)]
for _ in range(n):
  a,b = input().split()
  for i in range(min(len(a),len(b))):
    if a[i] != b[i]:
      l[orda(a[i])].add(orda(b[i]))
      r[orda(b[i])].add(orda(a[i]))
      break
  else:
    if len(a) > len(b):
      print(-1)
      exit()
for i in range(26):
  r[i] = len(r[i])
t = []
for z in range(26):
  if not r[z]:
    h.heappush(t,z)
while t:
  cur = h.heappop(t)
  ans.append(cur)
  for x in l[cur]:
    r[x] -= 1
    if not r[x]:
      h.heappush(t,x)
alp = lambda n: chr(n+97)
pt = "".join(map(alp,ans))
if len(pt) != 26:
  pt = -1
print(pt)

Submission Info

Judge Result