How to resolve the algorithm Greatest subsequential sum step by step in the Oberon-2 programming language

Published on 12 May 2024 09:40 PM
#Oberon-2

How to resolve the algorithm Greatest subsequential sum step by step in the Oberon-2 programming language

Table of Contents

Problem Statement

Given a sequence of integers, find a continuous subsequence which maximizes the sum of its elements, that is, the elements of no other single subsequence add up to a value larger than this one.

An empty subsequence is considered to have the sum of   0;   thus if all elements are negative, the result must be the empty sequence.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Greatest subsequential sum step by step in the Oberon-2 programming language

Source code in the oberon-2 programming language

MODULE GreatestSubsequentialSum;
IMPORT 
  Out, 
  Err,
  IntStr,
  ProgramArgs,
  TextRider;
TYPE  
  IntSeq= POINTER TO ARRAY OF LONGINT;

PROCEDURE ShowUsage();
BEGIN
  Out.String("Usage: GreatestSubsequentialSum {int}+");Out.Ln
END ShowUsage;

PROCEDURE Gss(iseq: IntSeq; VAR start, end, maxsum: LONGINT);
VAR
  i, j, sum: LONGINT;
BEGIN
  i := 0; maxsum := 0; start := 0; end := -1;
  WHILE (i < LEN(iseq^)) DO
    sum := 0; j := i;
    WHILE (j < LEN(iseq^) - 1) DO
      INC(sum,iseq[j]);
      IF sum > maxsum THEN
        maxsum := sum;
        start := i;
        end := j
      END;
      INC(j)
    END;
    INC(i)
  END
END Gss;


PROCEDURE GetParams():IntSeq;
VAR
  reader: TextRider.Reader;
  iseq: IntSeq;
  param: ARRAY 32 OF CHAR;
  argc,i: LONGINT;
  res: SHORTINT;
BEGIN
  iseq := NIL;
  reader := TextRider.ConnectReader(ProgramArgs.args);
  IF reader # NIL THEN
    argc := ProgramArgs.args.ArgNumber();
    IF argc < 1 THEN
      Err.String("There is no enough arguments.");Err.Ln;
      ShowUsage;
      HALT(0)
    END;

    reader.ReadLn; (* Skips program name *)

    NEW(iseq,argc);
    FOR i := 0 TO argc - 1 DO
      reader.ReadLine(param);
      IntStr.StrToInt(param,iseq[i],res);
    END   
 END;
 RETURN iseq
END GetParams;

PROCEDURE Do;
VAR
  iseq: IntSeq;
  start, end, sum, i: LONGINT;
BEGIN
  iseq := GetParams();
  Gss(iseq, start, end, sum);
  i := start;
  Out.String("[");
  WHILE (i <= end) DO
    Out.LongInt(iseq[i],0);
    IF (i < end) THEN Out.Char(',') END;
    INC(i)
  END;
  Out.String("]: ");Out.LongInt(sum,0);Out.Ln
END Do;

BEGIN
  Do
END GreatestSubsequentialSum.

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