// Another smarter approach would be to observe that the special numbers in the range are constant and that // the amount of them in the range 10 - 30 000 000 is not prohibitively large, so it is possible to precompute them using a basic approach and then hardcode them function solve(arr) { let solution = [10, 12, 21, 23, 32, 34, 43, 45, 54, 56, 65, 67, 76, 78, 87, 89, 98, 101, 121, 123, 210, 212, 232, 234, 321, 323, 343, 345, 432, 434, 454, 456, 543, 545, 565, 567, 654, 656, 676, 678, 765, 767, 787, 789, 876, 878, 898, 987, 989, 1010, 1012, 1210, 1212, 1232, 1234, 2101, 2121, 2123, 2321, 2323, 2343, 2345, 3210, 3212, 3232, 3234, 3432, 3434, 3454, 3456, 4321, 4323, 4343, 4345, 4543, 4545, 4565, 4567, 5432, 5434, 5454, 5456, 5654, 5656, 5676, 5678, 6543, 6545, 6565, 6567, 6765, 6767, 6787, 6789, 7654, 7656, 7676, 7678, 7876, 7878, 7898, 8765, 8767, 8787, 8789, 8987, 8989, 9876, 9878, 9898, 10101, 10121, 10123, 12101, 12121, 12123, 12321, 12323, 12343, 12345, 21010, 21012, 21210, 21212, 21232, 21234, 23210, 23212, 23232, 23234, 23432, 23434, 23454, 23456, 32101, 32121, 32123, 32321, 32323, 32343, 32345, 34321, 34323, 34343, 34345, 34543, 34545, 34565, 34567, 43210, 43212, 43232, 43234, 43432, 43434, 43454, 43456, 45432, 45434, 45454, 45456, 45654, 45656, 45676, 45678, 54321, 54323, 54343, 54345, 54543, 54545, 54565, 54567, 56543, 56545, 56565, 56567, 56765, 56767, 56787, 56789, 65432, 65434, 65454, 65456, 65654, 65656, 65676, 65678, 67654, 67656, 67676, 67678, 67876, 67878, 67898, 76543, 76545, 76565, 76567, 76765, 76767, 76787, 76789, 78765, 78767, 78787, 78789, 78987, 78989, 87654, 87656, 87676, 87678, 87876, 87878, 87898, 89876, 89878, 89898, 98765, 98767, 98787, 98789, 98987, 98989, 101010, 101012, 101210, 101212, 101232, 101234, 121010, 121012, 121210, 121212, 121232, 121234, 123210, 123212, 123232, 123234, 123432, 123434, 123454, 123456, 210101, 210121, 210123, 212101, 212121, 212123, 212321, 212323, 212343, 212345, 232101, 232121, 232123, 232321, 232323, 232343, 232345, 234321, 234323, 234343, 234345, 234543, 234545, 234565, 234567, 321010, 321012, 321210, 321212, 321232, 321234, 323210, 323212, 323232, 323234, 323432, 323434, 323454, 323456, 343210, 343212, 343232, 343234, 343432, 343434, 343454, 343456, 345432, 345434, 345454, 345456, 345654, 345656, 345676, 345678, 432101, 432121, 432123, 432321, 432323, 432343, 432345, 434321, 434323, 434343, 434345, 434543, 434545, 434565, 434567, 454321, 454323, 454343, 454345, 454543, 454545, 454565, 454567, 456543, 456545, 456565, 456567, 456765, 456767, 456787, 456789, 543210, 543212, 543232, 543234, 543432, 543434, 543454, 543456, 545432, 545434, 545454, 545456, 545654, 545656, 545676, 545678, 565432, 565434, 565454, 565456, 565654, 565656, 565676, 565678, 567654, 567656, 567676, 567678, 567876, 567878, 567898, 654321, 654323, 654343, 654345, 654543, 654545, 654565, 654567, 656543, 656545, 656565, 656567, 656765, 656767, 656787, 656789, 676543, 676545, 676565, 676567, 676765, 676767, 676787, 676789, 678765, 678767, 678787, 678789, 678987, 678989, 765432, 765434, 765454, 765456, 765654, 765656, 765676, 765678, 767654, 767656, 767676, 767678, 767876, 767878, 767898, 787654, 787656, 787676, 787678, 787876, 787878, 787898, 789876, 789878, 789898, 876543, 876545, 876565, 876567, 876765, 876767, 876787, 876789, 878765, 878767, 878787, 878789, 878987, 878989, 898765, 898767, 898787, 898789, 898987, 898989, 987654, 987656, 987676, 987678, 987876, 987878, 987898, 989876, 989878, 989898, 1010101, 1010121, 1010123, 1012101, 1012121, 1012123, 1012321, 1012323, 1012343, 1012345, 1210101, 1210121, 1210123, 1212101, 1212121, 1212123, 1212321, 1212323, 1212343, 1212345, 1232101, 1232121, 1232123, 1232321, 1232323, 1232343, 1232345, 1234321, 1234323, 1234343, 1234345, 1234543, 1234545, 1234565, 1234567, 2101010, 2101012, 2101210, 2101212, 2101232, 2101234, 2121010, 2121012, 2121210, 2121212, 2121232, 2121234, 2123210, 2123212, 2123232, 2123234, 2123432, 2123434, 2123454, 2123456, 2321010, 2321012, 2321210, 2321212, 2321232, 2321234, 2323210, 2323212, 2323232, 2323234, 2323432, 2323434, 2323454, 2323456, 2343210, 2343212, 2343232, 2343234, 2343432, 2343434, 2343454, 2343456, 2345432, 2345434, 2345454, 2345456, 2345654, 2345656, 2345676, 2345678, 3210101, 3210121, 3210123, 3212101, 3212121, 3212123, 3212321, 3212323, 3212343, 3212345, 3232101, 3232121, 3232123, 3232321, 3232323, 3232343, 3232345, 3234321, 3234323, 3234343, 3234345, 3234543, 3234545, 3234565, 3234567, 3432101, 3432121, 3432123, 3432321, 3432323, 3432343, 3432345, 3434321, 3434323, 3434343, 3434345, 3434543, 3434545, 3434565, 3434567, 3454321, 3454323, 3454343, 3454345, 3454543, 3454545, 3454565, 3454567, 3456543, 3456545, 3456565, 3456567, 3456765, 3456767, 3456787, 3456789, 4321010, 4321012, 4321210, 4321212, 4321232, 4321234, 4323210, 4323212, 4323232, 4323234, 4323432, 4323434, 4323454, 4323456, 4343210, 4343212, 4343232, 4343234, 4343432, 4343434, 4343454, 4343456, 4345432, 4345434, 4345454, 4345456, 4345654, 4345656, 4345676, 4345678, 4543210, 4543212, 4543232, 4543234, 4543432, 4543434, 4543454, 4543456, 4545432, 4545434, 4545454, 4545456, 4545654, 4545656, 4545676, 4545678, 4565432, 4565434, 4565454, 4565456, 4565654, 4565656, 4565676, 4565678, 4567654, 4567656, 4567676, 4567678, 4567876, 4567878, 4567898, 5432101, 5432121, 5432123, 5432321, 5432323, 5432343, 5432345, 5434321, 5434323, 5434343, 5434345, 5434543, 5434545, 5434565, 5434567, 5454321, 5454323, 5454343, 5454345, 5454543, 5454545, 5454565, 5454567, 5456543, 5456545, 5456565, 5456567, 5456765, 5456767, 5456787, 5456789, 5654321, 5654323, 5654343, 5654345, 5654543, 5654545, 5654565, 5654567, 5656543, 5656545, 5656565, 5656567, 5656765, 5656767, 5656787, 5656789, 5676543, 5676545, 5676565, 5676567, 5676765, 5676767, 5676787, 5676789, 5678765, 5678767, 5678787, 5678789, 5678987, 5678989, 6543210, 6543212, 6543232, 6543234, 6543432, 6543434, 6543454, 6543456, 6545432, 6545434, 6545454, 6545456, 6545654, 6545656, 6545676, 6545678, 6565432, 6565434, 6565454, 6565456, 6565654, 6565656, 6565676, 6565678, 6567654, 6567656, 6567676, 6567678, 6567876, 6567878, 6567898, 6765432, 6765434, 6765454, 6765456, 6765654, 6765656, 6765676, 6765678, 6767654, 6767656, 6767676, 6767678, 6767876, 6767878, 6767898, 6787654, 6787656, 6787676, 6787678, 6787876, 6787878, 6787898, 6789876, 6789878, 6789898, 7654321, 7654323, 7654343, 7654345, 7654543, 7654545, 7654565, 7654567, 7656543, 7656545, 7656565, 7656567, 7656765, 7656767, 7656787, 7656789, 7676543, 7676545, 7676565, 7676567, 7676765, 7676767, 7676787, 7676789, 7678765, 7678767, 7678787, 7678789, 7678987, 7678989, 7876543, 7876545, 7876565, 7876567, 7876765, 7876767, 7876787, 7876789, 7878765, 7878767, 7878787, 7878789, 7878987, 7878989, 7898765, 7898767, 7898787, 7898789, 7898987, 7898989, 8765432, 8765434, 8765454, 8765456, 8765654, 8765656, 8765676, 8765678, 8767654, 8767656, 8767676, 8767678, 8767876, 8767878, 8767898, 8787654, 8787656, 8787676, 8787678, 8787876, 8787878, 8787898, 8789876, 8789878, 8789898, 8987654, 8987656, 8987676, 8987678, 8987876, 8987878, 8987898, 8989876, 8989878, 8989898, 9876543, 9876545, 9876565, 9876567, 9876765, 9876767, 9876787, 9876789, 9878765, 9878767, 9878787, 9878789, 9878987, 9878989, 9898765, 9898767, 9898787, 9898789, 9898987, 9898989, 10101010, 10101012, 10101210, 10101212, 10101232, 10101234, 10121010, 10121012, 10121210, 10121212, 10121232, 10121234, 10123210, 10123212, 10123232, 10123234, 10123432, 10123434, 10123454, 10123456, 12101010, 12101012, 12101210, 12101212, 12101232, 12101234, 12121010, 12121012, 12121210, 12121212, 12121232, 12121234, 12123210, 12123212, 12123232, 12123234, 12123432, 12123434, 12123454, 12123456, 12321010, 12321012, 12321210, 12321212, 12321232, 12321234, 12323210, 12323212, 12323232, 12323234, 12323432, 12323434, 12323454, 12323456, 12343210, 12343212, 12343232, 12343234, 12343432, 12343434, 12343454, 12343456, 12345432, 12345434, 12345454, 12345456, 12345654, 12345656, 12345676, 12345678, 21010101, 21010121, 21010123, 21012101, 21012121, 21012123, 21012321, 21012323, 21012343, 21012345, 21210101, 21210121, 21210123, 21212101, 21212121, 21212123, 21212321, 21212323, 21212343, 21212345, 21232101, 21232121, 21232123, 21232321, 21232323, 21232343, 21232345, 21234321, 21234323, 21234343, 21234345, 21234543, 21234545, 21234565, 21234567, 23210101, 23210121, 23210123, 23212101, 23212121, 23212123, 23212321, 23212323, 23212343, 23212345, 23232101, 23232121, 23232123, 23232321, 23232323, 23232343, 23232345, 23234321, 23234323, 23234343, 23234345, 23234543, 23234545, 23234565, 23234567, 23432101, 23432121, 23432123, 23432321, 23432323, 23432343, 23432345, 23434321, 23434323, 23434343, 23434345, 23434543, 23434545, 23434565, 23434567, 23454321, 23454323, 23454343, 23454345, 23454543, 23454545, 23454565, 23454567, 23456543, 23456545, 23456565, 23456567, 23456765, 23456767, 23456787, 23456789]; let minString = arr.shift(); let maxString = arr.shift(); let min = Number.parseInt(minString); let max = Number.parseInt(maxString); for (let i = 0; i < solution.length; i++) { if (solution[i] < min) { continue; } if (solution[i] > max) { break; } console.log(solution[i]); } }