def triangles(creation_sequence):
 cs = creation_sequence
 dr = cs.count('d')
 ntri = (((dr * (dr - 1)) * (dr - 2)) / 6)
 for (i, typ) in enumerate(cs):
  if (typ == 'i'):
   ntri += ((dr * (dr - 1)) / 2)
  else:
   dr -= 1
 return ntri

def triangles ( creation_sequence ) : cs = creation_sequence dr = cs . count ( 'd' ) ntri = ( ( ( dr * ( dr - 1 ) ) * ( dr - 2 ) ) / 6 ) for ( i , typ ) in enumerate ( cs ) : if ( typ == 'i' ) : ntri += ( ( dr * ( dr - 1 ) ) / 2 ) else : dr -= 1 return ntri
compute number of triangles in the threshold graph with the given creation sequence .