루비-재귀 버전-52
r=->(n,v=nil){(n-=1;n<0 ?v:r[n,(v ?[n,v]:[n])])||[]}
비 재귀 버전 : 66 62 57
r=->i{(i-1).downto(0).inject(nil){|a,n|a ?[n,a]:[n]}||[]}
샘플 출력 (두 버전 모두 동일)
p r[0] # => []
p r[1] # => [0]
p r[2] # => [0, [1]]
p r[6] # => [0, [1, [2, [3, [4, [5]]]]]]
p r[26] # => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25]]]]]]]]]]]]]]]]]]]]]]]]]]
p r[69] # => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25, [26, [27, [28, [29, [30, [31, [32, [33, [34, [35, [36, [37, [38, [39, [40, [41, [42, [43, [44, [45, [46, [47, [48, [49, [50, [51, [52, [53, [54, [55, [56, [57, [58, [59, [60, [61, [62, [63, [64, [65, [66, [67, [68]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]
비 재귀 버전은 임의로 큰 입력을 처리 할 수 있습니다.
p r[1000] # => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25, [26, [27, [28, [29, [30, [31, [32, [33, [34, [35, [36, [37, [38, [39, [40, [41, [42, [43, [44, [45, [46, [47, [48, [49, [50, [51, [52, [53, [54, [55, [56, [57, [58, [59, [60, [61, [62, [63, [64, [65, [66, [67, [68, [69, [70, [71, [72, [73, [74, [75, [76, [77, [78, [79, [80, [81, [82, [83, [84, [85, [86, [87, [88, [89, [90, [91, [92, [93, [94, [95, [96, [97, [98, [99, [100, [101, [102, [103, [104, [105, [106, [107, [108, [109, [110, [111, [112, [113, [114, [115, [116, [117, [118, [119, [120, [121, [122, [123, [124, [125, [126, [127, [128, [129, [130, [131, [132, [133, [134, [135, [136, [137, [138, [139, [140, [141, [142, [143, [144, [145, [146, [147, [148, [149, [150, [151, [152, [153, [154, [155, [156, [157, [158, [159, [160, [161, [162, [163, [164, [165, [166, [167, [168, [169, [170, [171, [172, [173, [174, [175, [176, [177, [178, [179, [180, [181, [182, [183, [184, [185, [186, [187, [188, [189, [190, [191, [192, [193, [194, [195, [196, [197, [198, [199, [200, [201, [202, [203, [204, [205, [206, [207, [208, [209, [210, [211, [212, [213, [214, [215, [216, [217, [218, [219, [220, [221, [222, [223, [224, [225, [226, [227, [228, [229, [230, [231, [232, [233, [234, [235, [236, [237, [238, [239, [240, [241, [242, [243, [244, [245, [246, [247, [248, [249, [250, [251, [252, [253, [254, [255, [256, [257, [258, [259, [260, [261, [262, [263, [264, [265, [266, [267, [268, [269, [270, [271, [272, [273, [274, [275, [276, [277, [278, [279, [280, [281, [282, [283, [284, [285, [286, [287, [288, [289, [290, [291, [292, [293, [294, [295, [296, [297, [298, [299, [300, [301, [302, [303, [304, [305, [306, [307, [308, [309, [310, [311, [312, [313, [314, [315, [316, [317, [318, [319, [320, [321, [322, [323, [324, [325, [326, [327, [328, [329, [330, [331, [332, [333, [334, [335, [336, [337, [338, [339, [340, [341, [342, [343, [344, [345, [346, [347, [348, [349, [350, [351, [352, [353, [354, [355, [356, [357, [358, [359, [360, [361, [362, [363, [364, [365, [366, [367, [368, [369, [370, [371, [372, [373, [374, [375, [376, [377, [378, [379, [380, [381, [382, [383, [384, [385, [386, [387, [388, [389, [390, [391, [392, [393, [394, [395, [396, [397, [398, [399, [400, [401, [402, [403, [404, [405, [406, [407, [408, [409, [410, [411, [412, [413, [414, [415, [416, [417, [418, [419, [420, [421, [422, [423, [424, [425, [426, [427, [428, [429, [430, [431, [432, [433, [434, [435, [436, [437, [438, [439, [440, [441, [442, [443, [444, [445, [446, [447, [448, [449, [450, [451, [452, [453, [454, [455, [456, [457, [458, [459, [460, [461, [462, [463, [464, [465, [466, [467, [468, [469, [470, [471, [472, [473, [474, [475, [476, [477, [478, [479, [480, [481, [482, [483, [484, [485, [486, [487, [488, [489, [490, [491, [492, [493, [494, [495, [496, [497, [498, [499, [500, [501, [502, [503, [504, [505, [506, [507, [508, [509, [510, [511, [512, [513, [514, [515, [516, [517, [518, [519, [520, [521, [522, [523, [524, [525, [526, [527, [528, [529, [530, [531, [532, [533, [534, [535, [536, [537, [538, [539, [540, [541, [542, [543, [544, [545, [546, [547, [548, [549, [550, [551, [552, [553, [554, [555, [556, [557, [558, [559, [560, [561, [562, [563, [564, [565, [566, [567, [568, [569, [570, [571, [572, [573, [574, [575, [576, [577, [578, [579, [580, [581, [582, [583, [584, [585, [586, [587, [588, [589, [590, [591, [592, [593, [594, [595, [596, [597, [598, [599, [600, [601, [602, [603, [604, [605, [606, [607, [608, [609, [610, [611, [612, [613, [614, [615, [616, [617, [618, [619, [620, [621, [622, [623, [624, [625, [626, [627, [628, [629, [630, [631, [632, [633, [634, [635, [636, [637, [638, [639, [640, [641, [642, [643, [644, [645, [646, [647, [648, [649, [650, [651, [652, [653, [654, [655, [656, [657, [658, [659, [660, [661, [662, [663, [664, [665, [666, [667, [668, [669, [670, [671, [672, [673, [674, [675, [676, [677, [678, [679, [680, [681, [682, [683, [684, [685, [686, [687, [688, [689, [690, [691, [692, [693, [694, [695, [696, [697, [698, [699, [700, [701, [702, [703, [704, [705, [706, [707, [708, [709, [710, [711, [712, [713, [714, [715, [716, [717, [718, [719, [720, [721, [722, [723, [724, [725, [726, [727, [728, [729, [730, [731, [732, [733, [734, [735, [736, [737, [738, [739, [740, [741, [742, [743, [744, [745, [746, [747, [748, [749, [750, [751, [752, [753, [754, [755, [756, [757, [758, [759, [760, [761, [762, [763, [764, [765, [766, [767, [768, [769, [770, [771, [772, [773, [774, [775, [776, [777, [778, [779, [780, [781, [782, [783, [784, [785, [786, [787, [788, [789, [790, [791, [792, [793, [794, [795, [796, [797, [798, [799, [800, [801, [802, [803, [804, [805, [806, [807, [808, [809, [810, [811, [812, [813, [814, [815, [816, [817, [818, [819, [820, [821, [822, [823, [824, [825, [826, [827, [828, [829, [830, [831, [832, [833, [834, [835, [836, [837, [838, [839, [840, [841, [842, [843, [844, [845, [846, [847, [848, [849, [850, [851, [852, [853, [854, [855, [856, [857, [858, [859, [860, [861, [862, [863, [864, [865, [866, [867, [868, [869, [870, [871, [872, [873, [874, [875, [876, [877, [878, [879, [880, [881, [882, [883, [884, [885, [886, [887, [888, [889, [890, [891, [892, [893, [894, [895, [896, [897, [898, [899, [900, [901, [902, [903, [904, [905, [906, [907, [908, [909, [910, [911, [912, [913, [914, [915, [916, [917, [918, [919, [920, [921, [922, [923, [924, [925, [926, [927, [928, [929, [930, [931, [932, [933, [934, [935, [936, [937, [938, [939, [940, [941, [942, [943, [944, [945, [946, [947, [948, [949, [950, [951, [952, [953, [954, [955, [956, [957, [958, [959, [960, [961, [962, [963, [964, [965, [966, [967, [968, [969, [970, [971, [972, [973, [974, [975, [976, [977, [978, [979, [980, [981, [982, [983, [984, [985, [986, [987, [988, [989, [990, [991, [992, [993, [994, [995, [996, [997, [998, [999]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]
두 버전 모두 음수를 정상적으로 받아들입니다.
p r[-5] # => []