Selection Sort

Selection Sort works by repeatedly selecting the smallest element from the unsorted portion of the dataset and appending it to the end of the sorted portion.

In the first pass, the smallest value is found and moved to the 0 index. The remainder of the unsorted array is then searched for the new minimum, which is placed in the 1 index, and so on. For an array of n elements, this will require n passes.

Steps:

• Find the smallest element from the unsorted portion of the list.
• Append this element to the end of the sorted portion.
• Repeat this process until the entire list is sorted.

Example:

TRObject Syntax

  var
    arr: array[0..6] of Integer;
    i, j, minIdx, n, temp: Integer;
    str: string;
  
  void selectionSort;
  {
      n = Length(arr);
      for (i = 0 to n - 1)
      {
          minIdx = i;
          for (j = i + 1 to n - 1)
          {
              if (arr[j] < arr[minIdx])
              {
                  minIdx = j;
              }
          }
          
          temp = arr[minIdx];
          arr[minIdx] = arr[i];
          arr[i] = temp;
      }
  }
  
  {
    arr[0] = 12;
    arr[1] = 11;
    arr[2] = 13;
    arr[3] = 5;
    arr[4] = 1;
    arr[5] = 7;
    arr[6] = 9;
  
    str = 'Unordered array: ';
    
    for (i = 0 to Length(arr)-1)
    {
      str = str + IntToStr(arr[i]) + ' ';
    }  
    
    ShowMessage(str);
  
    selectionSort;
    str = 'Array sorted from smallest to largest: ';
  
    for (i = 0 to Length(arr)-1)
    {
      str = str + IntToStr(arr[i]) + ' ';
    }
    ShowMessage(str);
  
    str = 'Array sorted from largest to smallest: ';  
    
    for (i = Length(arr)-1 downto 0)
    {
      str = str + IntToStr(arr[i]) + ' ';
    }
    ShowMessage(str);
  }

Base Syntax

  var
    arr: array[0..6] of Integer;
    i, j, minIdx, n, temp: Integer;
    str: string;
  
  procedure selectionSort;
  begin
      n := Length(arr);
      for i := 0 to n - 1 do 
      begin
          minIdx := i;
          for j := i + 1 to n - 1 do
          begin
              if arr[j] < arr[minIdx] then
              begin
                  minIdx := j;
              end;
          end;
          
          temp := arr[minIdx];
          arr[minIdx] := arr[i];
          arr[i] := temp;
      end;
  end;
  
  begin
    arr[0] := 12;
    arr[1] := 11;
    arr[2] := 13;
    arr[3] := 5;
    arr[4] := 1;
    arr[5] := 7;
    arr[6] := 9;
  
    str := 'Unordered array: ';
    
    for i := 0 to Length(arr)-1 do
    begin
      str := str + IntToStr(arr[i]) + ' ';
    end;  
    
    ShowMessage(str);
  
    selectionSort;
    str := 'Array sorted from smallest to largest: ';
  
    for i := 0 to Length(arr)-1 do
    begin
      str := str + IntToStr(arr[i]) + ' ';
    end;
    ShowMessage(str);
  
    str := 'Array sorted from largest to smallest: ';  
    
    for i := Length(arr)-1 downto 0 do
    begin
      str := str + IntToStr(arr[i]) + ' ';
    end;
    ShowMessage(str);
  end;

See Also

• Sorting Algorithms
• TclArray
• Arrays