Initially , frequencies of ' a ' , ' b ' , ' c ' and ' d ' are 0.
if ( ( 0 , 0 ) , ( 0 , 0 ) ) in mp : NEW_LINE INDENT mp [ ( 0 , 0 ) , ( 0 , 0 ) ] += 1 NEW_LINE DEDENT else : NEW_LINE INDENT mp [ ( 0 , 0 ) , ( 0 , 0 ) ] = 1 NEW_LINE DEDENT