Question

How to implement binary search in Pascal

Answer 1

program BinarySearchDemo;

const
  size = 8;
  arr: array[1..size] of integer = (2, 3, 6, 7, 12, 15, 17, 19);

function BinarySearch(to_find: integer): integer;
var
  left, right, mid: integer;
begin
  left := 1;
  right := size;

  while left <= right do
  begin
    mid := left + (right - left) div 2;

    if arr[mid] = to_find then
    begin
      BinarySearch := mid - 1;  // Return 0-based index like in C 
      exit;
    end;

    if arr[mid] < to_find then
      left := mid + 1
    else
      right := mid - 1;
  end;

  BinarySearch := -1;
end;

var
  to_find, index: integer;

begin
  to_find := 7;
  index := BinarySearch(to_find);

  if index = -1 then
    writeln('not found')
  else
    writeln('Found at index: ', index);
end.



(*
run:

Found at index: 3

*)

 

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