Data commit

Task/Partition-function-P/Delphi/partition-function-p.delphi

@@ -0,0 +1,69 @@
+program Partition_function_P;
+
+{$APPTYPE CONSOLE}
+
+uses
+  System.SysUtils,
+  Velthuis.BigIntegers,
+  System.Diagnostics;
+
+var
+  p: TArray<BigInteger>;
+  pd: TArray<Integer>;
+
+function PartiDiffDiff(n: Integer): Integer;
+begin
+  if n and 1 = 1 then
+    exit((n + 1) div 2);
+  Result := n + 1;
+end;
+
+function partDiff(n: Integer): Integer;
+begin
+  if n < 2 then
+    exit(1);
+
+  pd[n] := pd[n - 1] + PartiDiffDiff(n - 1);
+  Result := pd[n];
+end;
+
+procedure partitionP(n: Integer);
+begin
+  if n < 2 then
+    exit;
+
+  var psum: BigInteger := 0;
+  for var i := 1 to n do
+  begin
+    var pdi := partDiff(i);
+    if pdi > n then
+      Break;
+
+    var sign: Int64 := -1;
+
+    if (i - 1) mod 4 < 2 then
+      sign := 1;
+
+    var t: BigInteger := BigInteger(p[n - pdi]) * BigInteger(sign);
+    psum := psum + t;
+  end;
+  p[n] := psum;
+end;
+
+begin
+  var stopwatch := TStopwatch.Create;
+  const n = 6666;
+  SetLength(p, n + 1);
+  SetLength(pd, n + 1);
+  stopwatch.Start;
+  p[0] := 1;
+  pd[0] := 1;
+  p[1] := 1;
+  pd[1] := 1;
+  for var i := 2 to n do
+    partitionP(i);
+  stopwatch.Stop;
+  writeln(format('p[%d] = %s', [n, p[n].ToString]));
+  writeln('Took ', stopwatch.ElapsedMilliseconds, 'ms');
+  Readln;
+end.