fork download 
  1. def palindromic_numbers
  2.   Enumerator.new do |y|
  3.     y << 0
  4.     #(1..).lazy.map {|k| [10 ** (k - 1), 10 ** k - 1].map(&:to_s)}.each do |b, e|
  5.     (1..Float::INFINITY).lazy.map {|k| [10 ** (k - 1), 10 ** k - 1].map(&:to_s)}.each do |b, e|
  6.       (b..e).lazy.each {|s| y << (s + s.reverse[1..-1]).to_i}
  7.       (b..e).lazy.each {|s| y << (s + s.reverse).to_i}
  8.     end
  9.   end
  10. end
  11. f = -> n {
  12.   ps = palindromic_numbers.each_cons(2).find {|a, b| a <= n && n <= b}
  13.   ps.map {|x| [(n - x).abs, x]}.sort.uniq.group_by(&:first).first.last.map(&:last)
  14. }
  15. p [0, 17, 100, 1000, 10000].map {|n| [n, f.(n)]}
  16. p palindromic_numbers.take(500)
Success #stdin #stdout 0.01s 8048KB
comments (?)
stdin 
Standard input is empty
stdout 
[[0, [0]], [17, [22]], [100, [99, 101]], [1000, [999, 1001]], [10000, [9999, 10001]]]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, 101, 111, 121, 131, 141, 151, 161, 171, 181, 191, 202, 212, 222, 232, 242, 252, 262, 272, 282, 292, 303, 313, 323, 333, 343, 353, 363, 373, 383, 393, 404, 414, 424, 434, 444, 454, 464, 474, 484, 494, 505, 515, 525, 535, 545, 555, 565, 575, 585, 595, 606, 616, 626, 636, 646, 656, 666, 676, 686, 696, 707, 717, 727, 737, 747, 757, 767, 777, 787, 797, 808, 818, 828, 838, 848, 858, 868, 878, 888, 898, 909, 919, 929, 939, 949, 959, 969, 979, 989, 999, 1001, 1111, 1221, 1331, 1441, 1551, 1661, 1771, 1881, 1991, 2002, 2112, 2222, 2332, 2442, 2552, 2662, 2772, 2882, 2992, 3003, 3113, 3223, 3333, 3443, 3553, 3663, 3773, 3883, 3993, 4004, 4114, 4224, 4334, 4444, 4554, 4664, 4774, 4884, 4994, 5005, 5115, 5225, 5335, 5445, 5555, 5665, 5775, 5885, 5995, 6006, 6116, 6226, 6336, 6446, 6556, 6666, 6776, 6886, 6996, 7007, 7117, 7227, 7337, 7447, 7557, 7667, 7777, 7887, 7997, 8008, 8118, 8228, 8338, 8448, 8558, 8668, 8778, 8888, 8998, 9009, 9119, 9229, 9339, 9449, 9559, 9669, 9779, 9889, 9999, 10001, 10101, 10201, 10301, 10401, 10501, 10601, 10701, 10801, 10901, 11011, 11111, 11211, 11311, 11411, 11511, 11611, 11711, 11811, 11911, 12021, 12121, 12221, 12321, 12421, 12521, 12621, 12721, 12821, 12921, 13031, 13131, 13231, 13331, 13431, 13531, 13631, 13731, 13831, 13931, 14041, 14141, 14241, 14341, 14441, 14541, 14641, 14741, 14841, 14941, 15051, 15151, 15251, 15351, 15451, 15551, 15651, 15751, 15851, 15951, 16061, 16161, 16261, 16361, 16461, 16561, 16661, 16761, 16861, 16961, 17071, 17171, 17271, 17371, 17471, 17571, 17671, 17771, 17871, 17971, 18081, 18181, 18281, 18381, 18481, 18581, 18681, 18781, 18881, 18981, 19091, 19191, 19291, 19391, 19491, 19591, 19691, 19791, 19891, 19991, 20002, 20102, 20202, 20302, 20402, 20502, 20602, 20702, 20802, 20902, 21012, 21112, 21212, 21312, 21412, 21512, 21612, 21712, 21812, 21912, 22022, 22122, 22222, 22322, 22422, 22522, 22622, 22722, 22822, 22922, 23032, 23132, 23232, 23332, 23432, 23532, 23632, 23732, 23832, 23932, 24042, 24142, 24242, 24342, 24442, 24542, 24642, 24742, 24842, 24942, 25052, 25152, 25252, 25352, 25452, 25552, 25652, 25752, 25852, 25952, 26062, 26162, 26262, 26362, 26462, 26562, 26662, 26762, 26862, 26962, 27072, 27172, 27272, 27372, 27472, 27572, 27672, 27772, 27872, 27972, 28082, 28182, 28282, 28382, 28482, 28582, 28682, 28782, 28882, 28982, 29092, 29192, 29292, 29392, 29492, 29592, 29692, 29792, 29892, 29992, 30003, 30103, 30203, 30303, 30403, 30503, 30603, 30703, 30803, 30903, 31013, 31113, 31213, 31313, 31413, 31513, 31613, 31713, 31813, 31913, 32023, 32123, 32223, 32323, 32423, 32523, 32623, 32723, 32823, 32923, 33033, 33133, 33233, 33333, 33433, 33533, 33633, 33733, 33833, 33933, 34043, 34143, 34243, 34343, 34443, 34543, 34643, 34743, 34843, 34943, 35053, 35153, 35253, 35353, 35453, 35553, 35653, 35753, 35853, 35953, 36063, 36163, 36263, 36363, 36463, 36563, 36663, 36763, 36863, 36963, 37073, 37173, 37273, 37373, 37473, 37573, 37673, 37773, 37873, 37973, 38083, 38183, 38283, 38383, 38483, 38583, 38683, 38783, 38883, 38983, 39093, 39193, 39293, 39393, 39493, 39593, 39693, 39793, 39893, 39993, 40004]
https://ideone.com/1zqSr1
language:
Ruby (ruby 2.5.5)
created:
87 days ago
visibility:
secret

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!