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class offer_book:
	def replaceBlank( p_str, rpl_str ):
		blank = ' '
		numOfBlank = 0
		originalLen = len( p_str )
		for char in p_str:
			if char == blank:
				numOfBlank += 1
		originalIndex = originalLen - 1
		newLen = originalLen + numOfBlank * ( len( rpl_str ) - len( blank ) )
		newIndex = newLen - 1
		newStr = [ blank ] * newLen
		while originalIndex >= 0:
			if p_str[ originalIndex ] == blank:
				newStr[ newIndex ] = '0'
				newIndex -= 1
				newStr[ newIndex ] = '2'
				newIndex -= 1
				newStr[ newIndex ] = '%'
				newIndex -= 1
			else:
				newStr[ newIndex ] = p_str[ originalIndex ]
				newIndex -= 1
			originalIndex -= 1
		return str( newStr )


newStr = offer_book.replaceBlank( ' we are happy! ', '%20' )
print( newStr )