Merge pull request #6602 from pokgopun/pwc175

pwc175 solution in dart

2 files changed, 78 insertions, 0 deletions

diff --git a/challenge-175/pokgopun/dart/ch-1.dart b/challenge-175/pokgopun/dart/ch-1.dart
new file mode 100644
index 0000000000..6317f2d8b4
--- /dev/null
+++ b/challenge-175/pokgopun/dart/ch-1.dart
@@ -0,0 +1,23 @@
+void main() {
+  print(LastWeekdayOfMonth(DateTime.sunday, 2022));
+}
+
+class LastWeekdayOfMonth {
+  final int weekday, year, month;
+  final data = <DateTime>[];
+  LastWeekdayOfMonth(this.weekday, this.year, [this.month = 0]) {
+    final mdc = _monthdayCount(year);
+    for (var i = 0; i < mdc.length; i++) {
+      var t = DateTime.utc(year, i + 1, mdc[i]);
+      var o = weekday - t.weekday;
+      data.add(t.add(Duration(days: o > 0 ? o - 7 : o)));
+    }
+  }
+  List<int> _monthdayCount(int year) =>
+      [31, year % 4 == 0 ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
+  @override
+  String toString() => [
+        if (month == 0) ...data,
+        if (month > 0 && month <= 12) data[month - 1]
+      ].map((dt) => dt.toString().split(" ")[0]).join("\n");
+}
diff --git a/challenge-175/pokgopun/dart/ch-2.dart b/challenge-175/pokgopun/dart/ch-2.dart
new file mode 100644
index 0000000000..e4bfd8847f
--- /dev/null
+++ b/challenge-175/pokgopun/dart/ch-2.dart
@@ -0,0 +1,55 @@
+int totient(int n) {
+  // totient(1) = 1, also handle totient(0) at the same time as it can be 0 or 1
+  if (n <= 1) {
+    return 1;
+  }
+  // calcuation using GCD
+  int r = 1; // 1 is relatively prime to any number
+  for (int i = 2; i < n; i++) {
+    if (gcdEuclidean(i, n) == 1) {
+      r++;
+    }
+  }
+  return r;
+}
+
+int gcdEuclidean(int a, int b) {
+  while (a != b) {
+    if (a > b) {
+      a -= b;
+    } else {
+      b -= a;
+    }
+  }
+  return a;
+}
+
+bool isPerfect(int n) {
+  if (n < 2 || n % 2 == 0) {
+    return false;
+  }
+  var sum = 1;
+  var t = totient(n);
+  while (t != 1) {
+    sum += t;
+    if (sum > n) {
+      return false;
+    }
+    t = totient(t);
+  }
+  return sum == n;
+}
+
+void main(List<String> args) {
+  int count = args.isNotEmpty ? int.parse(args[0]) : 20;
+  var output = "";
+  for (int i = 3; i < 50000; i++) {
+    if (isPerfect(i)) {
+      output += ", ${i.toString()}";
+      if (--count == 0) {
+        break;
+      }
+    }
+  }
+  print(output.substring(2));
+}