z-tickets
Toma, Strahinja and Uroš really like to place bets on horse races. Little Z. knows how much they like spending money on horse races, so he is trying to make them bet at his race track. In order to make them bet at his race track he decided that he will refund their bets for some serial numbers of the bet receipts.
The serial numbers contain N digits, where N is always divisible by 2. Mr. Little Z. says that he will refund the bet if the sum of the first N/2 digits of the serial number equals to the sum of the second N/2 digits of the serial number.
Little Z. is not sure if this is the best way to go, so he wants to find out, for a given N how many different serial numbers are there so that the sum of the first half of the digits equal to the sum of the second half of the digits.
4Output:
670If the receipts have 4 digit serial numbers, then there are 670 numbers for which Little Z has to refund the bet. Those are numbers: 0000, 0101, 0110, 1010, 1001, 1111 …then 659 more,and then .. 8989, 8998, 9898, 9889, 9999
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