De Bruijn sequences: Difference between revisions
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:* An OEIS entry: [https://oeis.org/A166315 A166315 lexicographically earliest binary de Bruijn sequences, B(2,n)] --- Not B(10,4), but possibly relevant.
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=={{header|C#}}==
{{trans|Kotlin}}
<lang csharp>using System;
using System.Collections.Generic;
using System.Text;
namespace DeBruijn {
class Program {
const string digits = "0123456789";
static string DeBruijn(int k, int n) {
var alphabet = digits.Substring(0, k);
var a = new byte[k * n];
var seq = new List<byte>();
void db(int t, int p) {
if (t > n) {
if (n % p == 0) {
seq.AddRange(new ArraySegment<byte>(a, 1, p));
}
} else {
a[t] = a[t - p];
db(t + 1, p);
var j = a[t - p] + 1;
while (j < k) {
a[t] = (byte)j;
db(t + 1, t);
j++;
}
}
}
db(1, 1);
var buf = new StringBuilder();
foreach (var i in seq) {
buf.Append(alphabet[i]);
}
var b = buf.ToString();
return b + b.Substring(0, n - 1);
}
static bool AllDigits(string s) {
foreach (var c in s) {
if (c < '0' || '9' < c) {
return false;
}
}
return true;
}
static void Validate(string db) {
var le = db.Length;
var found = new int[10_000];
var errs = new List<string>();
// Check all strings of 4 consecutive digits within 'db'
// to see if all 10,000 combinations occur without duplication.
for (int i = 0; i < le - 3; i++) {
var s = db.Substring(i, 4);
if (AllDigits(s)) {
int.TryParse(s, out int n);
found[n]++;
}
}
for (int i = 0; i < 10_000; i++) {
if (found[i] == 0) {
errs.Add(string.Format(" PIN number {0,4} missing", i));
} else if (found[i] > 1) {
errs.Add(string.Format(" PIN number {0,4} occurs {1} times", i, found[i]));
}
}
var lerr = errs.Count;
if (lerr == 0) {
Console.WriteLine(" No errors found");
} else {
var pl = lerr == 1 ? "" : "s";
Console.WriteLine(" {0} error{1} found:", lerr, pl);
errs.ForEach(Console.WriteLine);
}
}
static string Reverse(string s) {
char[] arr = s.ToCharArray();
Array.Reverse(arr);
return new string(arr);
}
static void Main() {
var db = DeBruijn(10, 4);
var le = db.Length;
Console.WriteLine("The length of the de Bruijn sequence is {0}", le);
Console.WriteLine("\nThe first 130 digits of the de Bruijn sequence are: {0}", db.Substring(0, 130));
Console.WriteLine("\nThe last 130 digits of the de Bruijn sequence are: {0}", db.Substring(le - 130, 130));
Console.WriteLine("\nValidating the deBruijn sequence:");
Validate(db);
Console.WriteLine("\nValidating the reversed deBruijn sequence:");
Validate(Reverse(db));
var bytes = db.ToCharArray();
bytes[4443] = '.';
db = new string(bytes);
Console.WriteLine("\nValidating the overlaid deBruijn sequence:");
Validate(db);
}
}
}</lang>
{{out}}
<pre>The length of the de Bruijn sequence is 10003
The first 130 digits of the de Bruijn sequence are: 0000100020003000400050006000700080009001100120013001400150016001700180019002100220023002400250026002700280029003100320033003400350
The last 130 digits of the de Bruijn sequence are: 6898689969697769786979698769886989699769986999777787779778877897798779978787978887889789878997979887989799879998888988998989999000
Validating the deBruijn sequence:
No errors found
Validating the reversed deBruijn sequence:
No errors found
Validating the overlaid deBruijn sequence:
4 errors found:
PIN number 1459 missing
PIN number 4591 missing
PIN number 5814 missing
PIN number 8145 missing</pre>
=={{header|Go}}==
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