Phone Numbers

August 15, 2017

Today’s task looks like homework:

Make a list of n-digit phone numbers according to the following rules:

1) First digit must not be zero.
2) First digit may be four, but no digits after the first may be four.
3) Any two consecutive digits must be different.
4) The user may specify any set of digits that may not appear in the phone number.

For instance, if n = 3 and the digits 1, 3, 5, 7, and 9 don’t appear in the output, the desired list of three-digit numbers starting with 2, 4, 6, or 8 followed by 0, 2, 6 or 8 without consecutive duplicates is: 202 206 208 260 262 268 280 282 286 402 406 408 420 426 428 460 462 468 480 482 486 602 606 608 620 626 628 680 682 686 802 806 808 820 826 828 860 862 868.

Your task is to write a program that generates phone numbers according to the rules given above. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

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