E=enumerate
def f(s):
 d={(x,y):v for x,r in E(s)for y,v in E(r)};q={(x,y):T[d[(x,y)]]for x,y in d if(' '==d[(x,y)])in(T:={d.get(V:=(x+X,y+Y),0):V for X,Y in[(1,0),(0,1),(-1,0),(0,-1)]})and d[(x,y)]in T};r={}
 while q:
  x,y=V=[*q][0];J,K=q.pop(V);X,Y=J-x,K-y;l=[]
  while d.get(W:=(x+X,y+Y),' ').isalpha():l+=d[W],;x,y=W;q.pop(W,0)
  r[d[V]]={*l}-{d[V]}
 q=[(T:=''.join(i for i in r if not r[i]),T)]
 for a,b in q:
  if''==(Q:=''.join(k for k in r if any(u in r[k]for u in a))):return b[::-1]
  q+=(Q,b+Q),
 
s1 = """
  R  
  R  
BBRBB
  R  
"""
s2 = """
    GY   
    GY   
RRRRGYRRR
    GY   
    GY   
BBBBBBBB
    GY  
    GY  
"""
s3 = """
    R    P 
    R    P 
AAAARAAAAPA
    R    P 
    R    P 
GGGGRGGG P 
    R      
"""
s4 = """
 O Y 
RRRYR
 O Y 
GOGGG
 O Y 
"""
s5 = """
YYYB
   B
   B
"""
def to_board(s):
	return [[*i] for i in filter(None, s.split('\n'))]
 
print(f(to_board(s1)))
print(f(to_board(s2)))
print(f(to_board(s3)))
print(f(to_board(s4)))
print(f(to_board(s5)))

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