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String.prototype.isPalindrome = function() {
  let t = this.toUpperCase();
  return t.split('').reverse().join('') === t;
}

function isPlausibleDate(y, m, d) {
  let p = new Date(y, m, d);
  return (
    p.getFullYear() == y &&
    p.getMonth() == m &&
    p.getDate() == d
  );
}

let out = [];
console.time();
for (let y = 2000; y <= 2999; y++)
  for (let m = 1; m <= 12; m++)
    for (let d = 1; d <= 31; d++) {
      let test = d.toString().padStart(2, '0') +
                 m.toString().padStart(2, '0') +
                 y.toString();
      if (test.isPalindrome()) {
        if (isPlausibleDate(y, m-1, d)) out.push([d, m, y].join('.'));
      }
    }
console.timeEnd();
console.log(out);
                

Lösung von: Lisa Salander (Heidi-Klum-Gymnasium Bottrop)

// NET 6.x | C# 10.x | VS-2022

static IEnumerable<DateOnly> GetPalindromeDates(DateSpan s) {
    while (s.Begin <= s.End) {
        var d = s.Begin.ToShortDateString().Replace(".", "");
        if (d == new string(d.Reverse().ToArray()))
            yield return s.Begin;
        s.Begin = s.Begin.AddDays(1);
    }
}

DateSpan s = new(new(2001, 1, 1), new(2999, 12, 31));
GetPalindromeDates(s).ToList().ForEach(x => Console.WriteLine(x.ToShortDateString()));

record struct DateSpan (DateOnly Begin, DateOnly End);
                

Lösung von: Jens Kelm (@JKooP)

#include <iostream>
#include <vector>
#include <boost/date_time/gregorian/gregorian.hpp>
using namespace boost::gregorian;

struct datespan { date begin; const date end; };

std::vector<date> get_palindrome_dates(datespan d) {
    std::vector<date>v;
    days add{ 1 };

    const auto get_leading_zero{ [](auto i) { std::stringstream ss; ss << 0 << i;
    return ss.str().substr(ss.str().length() - 2); } };

    while (d.begin < d.end) {
        const auto day_{ get_leading_zero(d.begin.day()) };
        const auto month_{ get_leading_zero(d.begin.month().as_number()) };
        std::stringstream ss;
        ss << day_ << month_ << d.begin.year();
        auto r{ ss.str() };
        std::reverse(r.begin(), r.end());
        if (r == ss.str())
            v.push_back(d.begin);
        d.begin += add;
    }
    return v;
}

int main() {
    const auto p{ get_palindrome_dates({ { 2000, 1, 1 }, { 2999, 12, 31 } }) };
    date_facet* f(new date_facet("%d.%m.%Y"));
    std::cout.imbue(std::locale(std::cout.getloc(), f));
    for (const auto& i : p)
        std::cout << i << "\n";
}
                

Lösung von: Jens Kelm (@JKooP)

' VBA-Funktion

Function GetPalindromeDates(ByVal first As Date, ByVal last As Date)
    Dim dates() As Variant
    Dim c As Integer
    Dim tmp As String
    Do While first < last
        tmp = Right("0" & Day(first), 2) & Right("0" & Month(first), 2) & Year(first)
        If tmp = StrReverse(tmp) Then
            ReDim Preserve dates(c)
            dates(c) = first
            c = c + 1
        End If
        first = DateAdd("d", 1, first)
    Loop
    GetPalindromeDates = dates
End Function

Sub Main()
    Const START_D As Date = #1/1/2000#
    Const END_D As Date = #12/31/2999#
    Dim dat As Variant
    For Each dat In GetPalindromeDates(START_D, END_D)
        Debug.Print dat
    Next
End Sub
                

Lösung von: Jens Kelm (@JKooP)