Calculate the prefix sum
if ( isPowerOfTwo ( a [ 0 ] ) ) : NEW_LINE INDENT prefix [ 0 ] = 1 NEW_LINE DEDENT for i in range ( 1 , n ) : NEW_LINE INDENT prefix [ i ] = prefix [ i - 1 ] NEW_LINE if ( isPowerOfTwo ( a [ i ] ) ) : NEW_LINE INDENT prefix [ i ] += 1 NEW_LINE DEDENT DEDENT