Upside-down numbers: Difference between revisions

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 ;* [[oeis:A299539|OEIS:A299539 - Upside-down numbers]]
+=={{header|Go}}==
+{{trans|Python}}
+{{libheader|Go-rcu}}
+<syntaxhighlight lang="go">package main
+import (
+    "fmt"
+    "rcu"
+)
+func genUpsideDown(limit int) chan int {
+    ch := make(chan int)
+    wrappings := [][2]int{
+        {1, 9}, {2, 8}, {3, 7}, {4, 6}, {5, 5},
+        {6, 4}, {7, 3}, {8, 2}, {9, 1},
+    }
+    evens := []int{19, 28, 37, 46, 55, 64, 73, 82, 91}
+    odds := []int{5}
+    oddIndex := 0
+    evenIndex := 0
+    ndigits := 1
+    pow := 100
+    count := 0
+    go func() {
+        for count < limit {
+            if ndigits%2 == 1 {
+                if len(odds) > oddIndex {
+                    ch <- odds[oddIndex]
+                    count++
+                    oddIndex++
+                } else {
+                    // build next odds, but switch to evens
+                    var nextOdds []int
+                    for _, w := range wrappings {
+                        for _, i := range odds {
+                            nextOdds = append(nextOdds, w[0]*pow+i*10+w[1])
+                        }
+                    }
+                    odds = nextOdds
+                    ndigits++
+                    pow *= 10
+                    oddIndex = 0
+                }
+            } else {
+                if len(evens) > evenIndex {
+                    ch <- evens[evenIndex]
+                    count++
+                    evenIndex++
+                } else {
+                    // build next evens, but switch to odds
+                    var nextEvens []int
+                    for _, w := range wrappings {
+                        for _, i := range evens {
+                            nextEvens = append(nextEvens, w[0]*pow+i*10+w[1])
+                        }
+                    }
+                    evens = nextEvens
+                    ndigits++
+                    pow *= 10
+                    evenIndex = 0
+                }
+            }
+        }
+        close(ch)
+    }()
+    return ch
+}
+func main() {
+    const limit = 50_000_000
+    count := 0
+    var ud50s []int
+    pow := 50
+    for n := range genUpsideDown(limit) {
+        count++
+        if count < 50 {
+            ud50s = append(ud50s, n)
+        } else if count == 50 {
+            ud50s = append(ud50s, n)
+            fmt.Println("First 50 upside down numbers:")
+            rcu.PrintTable(ud50s, 10, 5, true)
+            fmt.Println()
+            pow = 500
+        } else if count == pow {
+            fmt.Printf("%sth : %s\n", rcu.Commatize(pow), rcu.Commatize(n))
+            pow *= 10
+        }
+    }
+}</syntaxhighlight>
+{{out}}
+<pre>
+First 50 upside down numbers:
+19    28    37    46    55    64    73    82    91
+258   357   456   555   654   753   852   951 1,199
+,289 1,379 1,469 1,559 1,649 1,739 1,829 1,919 2,198 2,288
+,378 2,468 2,558 2,648 2,738 2,828 2,918 3,197 3,287 3,377
+,467 3,557 3,647 3,737 3,827 3,917 4,196 4,286 4,376 4,466
+th : 494,616
+,000th : 56,546,545
+,000th : 6,441,469,664
+,000th : 729,664,644,183
+,000,000th : 82,485,246,852,682
+,000,000th : 9,285,587,463,255,281
+</pre>
 =={{header|Pascal}}==
@@ Line 139: / Line 246: @@
 User time: 0.310 s CPU share: 99.30 %
 </pre>
 =={{header|Python}}==
 <syntaxhighlight lang="python">""" rosettacode.org task Upside-down_numbers """