Data commit

Task/De-Bruijn-sequences/Go/de-bruijn-sequences.go

@@ -0,0 +1,110 @@
+package main
+
+import (
+    "bytes"
+    "fmt"
+    "strconv"
+    "strings"
+)
+
+const digits = "0123456789"
+
+func deBruijn(k, n int) string {
+    alphabet := digits[0:k]
+    a := make([]byte, k*n)
+    var seq []byte
+    var db func(int, int) // recursive closure
+    db = func(t, p int) {
+        if t > n {
+            if n%p == 0 {
+                seq = append(seq, a[1:p+1]...)
+            }
+        } else {
+            a[t] = a[t-p]
+            db(t+1, p)
+            for j := int(a[t-p] + 1); j < k; j++ {
+                a[t] = byte(j)
+                db(t+1, t)
+            }
+        }
+    }
+    db(1, 1)
+    var buf bytes.Buffer
+    for _, i := range seq {
+        buf.WriteByte(alphabet[i])
+    }
+    b := buf.String()
+    return b + b[0:n-1] // as cyclic append first (n-1) digits
+}
+
+func allDigits(s string) bool {
+    for _, b := range s {
+        if b < '0' || b > '9' {
+            return false
+        }
+    }
+    return true
+}
+
+func validate(db string) {
+    le := len(db)
+    found := make([]int, 10000)
+    var errs []string
+    // Check all strings of 4 consecutive digits within 'db'
+    // to see if all 10,000 combinations occur without duplication.
+    for i := 0; i < le-3; i++ {
+        s := db[i : i+4]
+        if allDigits(s) {
+            n, _ := strconv.Atoi(s)
+            found[n]++
+        }
+    }
+    for i := 0; i < 10000; i++ {
+        if found[i] == 0 {
+            errs = append(errs, fmt.Sprintf("    PIN number %04d missing", i))
+        } else if found[i] > 1 {
+            errs = append(errs, fmt.Sprintf("    PIN number %04d occurs %d times", i, found[i]))
+        }
+    }
+    lerr := len(errs)
+    if lerr == 0 {
+        fmt.Println("  No errors found")
+    } else {
+        pl := "s"
+        if lerr == 1 {
+            pl = ""
+        }
+        fmt.Printf("  %d error%s found:\n", lerr, pl)
+        fmt.Println(strings.Join(errs, "\n"))
+    }
+}
+
+func reverse(s string) string {
+    bytes := []byte(s)
+    for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
+        bytes[i], bytes[j] = bytes[j], bytes[i]
+    }
+    return string(bytes)
+}
+
+func main() {
+    db := deBruijn(10, 4)
+    le := len(db)
+    fmt.Println("The length of the de Bruijn sequence is", le)
+    fmt.Println("\nThe first 130 digits of the de Bruijn sequence are:")
+    fmt.Println(db[0:130])
+    fmt.Println("\nThe last 130 digits of the de Bruijn sequence are:")
+    fmt.Println(db[le-130:])
+    fmt.Println("\nValidating the de Bruijn sequence:")
+    validate(db)
+
+    fmt.Println("\nValidating the reversed de Bruijn sequence:")
+    dbr := reverse(db)
+    validate(dbr)
+
+    bytes := []byte(db)
+    bytes[4443] = '.'
+    db = string(bytes)
+    fmt.Println("\nValidating the overlaid de Bruijn sequence:")
+    validate(db)
+}