Add Dijkstra in Pascal (TheRenegadeCoder#4829)

Author: pascalecu

archive/p/pascal/dijkstra.pas

@@ -0,0 +1,169 @@
+program Dijkstra;
+
+{$mode objfpc}{$H+}
+
+uses
+   Classes,
+   Generics.Collections,
+   Math,
+   SysUtils;
+
+type
+   TIntegerList = specialize TList<integer>;
+   TBooleanList = specialize TList<boolean>;
+
+procedure ShowUsage;
+begin
+   Writeln('Usage: please provide three inputs: a serialized matrix, a source node and a destination node');
+   Halt(1);
+end;
+
+function ParseIntegerList(const S: string): TIntegerList;
+var
+   Part: string;
+   Value: integer;
+begin
+   if S.Trim.IsEmpty then ShowUsage;
+   Result := TIntegerList.Create;
+   for Part in S.Split([',']) do
+   begin
+      if not TryStrToInt(Trim(Part), Value) or (Value < 0) then
+      begin
+         Result.Free;
+         ShowUsage;
+      end;
+      Result.Add(Value);
+   end;
+   if Result.Count = 0 then
+   begin
+      Result.Free;
+      ShowUsage;
+   end;
+end;
+
+// Checks if the matrix is square, returns dimension or -1 if invalid
+function MatrixDimension(const Matrix: TIntegerList): integer; inline;
+var
+   Len: integer;
+   D: integer;
+begin
+   Len := Matrix.Count;
+   D := Floor(Sqrt(Len));
+   if (D * D = Len) and (D > 0) then
+      Result := D
+   else
+      Result := -1;
+end;
+
+// Returns distance from src to dst or -1 if unreachable
+function Dijkstra(const Matrix: TIntegerList;
+   Dimension, Source, Destination: integer): integer;
+const
+   INF = $3F3F3F3F;
+var
+   Dist: TIntegerList;
+   Visited: TBooleanList;
+   I, J, MinDist, MinIndex, Weight, CurrentDist: integer;
+begin
+   Dist := TIntegerList.Create;
+   Visited := TBooleanList.Create;
+   try
+      Dist.Capacity := Dimension;
+      Visited.Capacity := Dimension;
+
+      for I := 0 to Dimension - 1 do
+      begin
+         Dist.Add(INF);
+         Visited.Add(False);
+      end;
+
+      Dist[Source] := 0;
+
+      for I := 0 to Dimension - 1 do
+      begin
+         MinDist := INF;
+         MinIndex := -1;
+
+         // Find closest unvisited node
+         for J := 0 to Dimension - 1 do
+            if (not Visited[J]) and (Dist[J] < MinDist) then
+            begin
+               MinDist := Dist[J];
+               MinIndex := J;
+            end;
+
+         if MinIndex = -1 then
+            Break;
+
+         Visited[MinIndex] := True;
+         CurrentDist := Dist[MinIndex];
+
+         if MinIndex = Destination then
+         begin
+            Result := CurrentDist;
+            Exit;
+         end;
+
+         for J := 0 to Dimension - 1 do
+         begin
+            Weight := Matrix[MinIndex * Dimension + J];
+            if (not Visited[J]) and (Weight > 0) and
+               (CurrentDist + Weight < Dist[J]) then
+               Dist[J] := CurrentDist + Weight;
+         end;
+      end;
+
+      if Dist[Destination] = INF then
+         Result := -1
+      else
+         Result := Dist[Destination];
+
+   finally
+      Dist.Free;
+      Visited.Free;
+   end;
+end;
+
+
+var
+   MatrixStr, SourceStr, DestinationStr: string;
+   Matrix: TIntegerList;
+   Dimension, Source, Destination, ShortestDistance: integer;
+begin
+   if ParamCount <> 3 then
+      ShowUsage;
+
+   MatrixStr := Trim(ParamStr(1));
+   SourceStr := Trim(ParamStr(2));
+   DestinationStr := Trim(ParamStr(3));
+
+   if (MatrixStr = '') or (SourceStr = '') or (DestinationStr = '') then
+      ShowUsage;
+
+   Matrix := nil;
+   try
+      Matrix := ParseIntegerList(MatrixStr);
+
+      Dimension := MatrixDimension(Matrix);
+
+      // Check if:
+      // - the matrix represents a valid square adjacency matrix (dimension <> 1)
+      // - the source and destination nodes are valid integers
+      // - the nodes are within valid index range [0, Dimension - 1]
+      if (Dimension = -1) or (not TryStrToInt(SourceStr, Source)) or
+         (not TryStrToInt(DestinationStr, Destination)) or (Source < 0) or
+         (Source >= Dimension) or (Destination < 0) or (Destination >= Dimension) then
+
+         ShowUsage;
+
+      ShortestDistance := Dijkstra(Matrix, Dimension, Source, Destination);
+
+      if ShortestDistance = -1 then
+         ShowUsage
+      else
+         Writeln(ShortestDistance);
+
+   finally
+      Matrix.Free;
+   end;
+end.