f = ->x{x>100 ? x-10 : 91.times.reduce(x+901){|r,_|r=f[r]}} puts (1..200).map{|i|"%3s -> %3s" % [i, f[i]]}
Standard input is empty
1 -> 91 2 -> 91 3 -> 91 4 -> 91 5 -> 91 6 -> 91 7 -> 91 8 -> 91 9 -> 91 10 -> 91 11 -> 91 12 -> 91 13 -> 91 14 -> 91 15 -> 91 16 -> 91 17 -> 91 18 -> 91 19 -> 91 20 -> 91 21 -> 91 22 -> 91 23 -> 91 24 -> 91 25 -> 91 26 -> 91 27 -> 91 28 -> 91 29 -> 91 30 -> 91 31 -> 91 32 -> 91 33 -> 91 34 -> 91 35 -> 91 36 -> 91 37 -> 91 38 -> 91 39 -> 91 40 -> 91 41 -> 91 42 -> 91 43 -> 91 44 -> 91 45 -> 91 46 -> 91 47 -> 91 48 -> 91 49 -> 91 50 -> 91 51 -> 91 52 -> 91 53 -> 91 54 -> 91 55 -> 91 56 -> 91 57 -> 91 58 -> 91 59 -> 91 60 -> 91 61 -> 91 62 -> 91 63 -> 91 64 -> 91 65 -> 91 66 -> 91 67 -> 91 68 -> 91 69 -> 91 70 -> 91 71 -> 91 72 -> 91 73 -> 91 74 -> 91 75 -> 91 76 -> 91 77 -> 91 78 -> 91 79 -> 91 80 -> 91 81 -> 91 82 -> 91 83 -> 91 84 -> 91 85 -> 91 86 -> 91 87 -> 91 88 -> 91 89 -> 91 90 -> 91 91 -> 91 92 -> 91 93 -> 91 94 -> 91 95 -> 91 96 -> 91 97 -> 91 98 -> 91 99 -> 91 100 -> 91 101 -> 91 102 -> 92 103 -> 93 104 -> 94 105 -> 95 106 -> 96 107 -> 97 108 -> 98 109 -> 99 110 -> 100 111 -> 101 112 -> 102 113 -> 103 114 -> 104 115 -> 105 116 -> 106 117 -> 107 118 -> 108 119 -> 109 120 -> 110 121 -> 111 122 -> 112 123 -> 113 124 -> 114 125 -> 115 126 -> 116 127 -> 117 128 -> 118 129 -> 119 130 -> 120 131 -> 121 132 -> 122 133 -> 123 134 -> 124 135 -> 125 136 -> 126 137 -> 127 138 -> 128 139 -> 129 140 -> 130 141 -> 131 142 -> 132 143 -> 133 144 -> 134 145 -> 135 146 -> 136 147 -> 137 148 -> 138 149 -> 139 150 -> 140 151 -> 141 152 -> 142 153 -> 143 154 -> 144 155 -> 145 156 -> 146 157 -> 147 158 -> 148 159 -> 149 160 -> 150 161 -> 151 162 -> 152 163 -> 153 164 -> 154 165 -> 155 166 -> 156 167 -> 157 168 -> 158 169 -> 159 170 -> 160 171 -> 161 172 -> 162 173 -> 163 174 -> 164 175 -> 165 176 -> 166 177 -> 167 178 -> 168 179 -> 169 180 -> 170 181 -> 171 182 -> 172 183 -> 173 184 -> 174 185 -> 175 186 -> 176 187 -> 177 188 -> 178 189 -> 179 190 -> 180 191 -> 181 192 -> 182 193 -> 183 194 -> 184 195 -> 185 196 -> 186 197 -> 187 198 -> 188 199 -> 189 200 -> 190