Threaded Mode | Linear Mode

***drdebcol*** · (This post was last modified: 08-08-2009 12:09 AM by drdebcol.)

There is man named Mabu who switches on-off the lights along a corridor at one university. Every bulb has its own toggle switch that changes the state of the light. If the light is off, pressing the switch turns it on. Pressing it again will turn it off. Initially each bulb is off. He does a peculiar thing. If there are n bulbs in a corridor, he walks along the corridor back and forth n times. On the ith walk, he toggles only the switches whose position
is divisible by i. He does not press any switch when coming back to his initial position. The ith walk is defined as going down the corridor (doing his peculiar thing) and coming back again. Determine the final state of the last bulb. Is it on or off?
Input
The input will be an integer indicating the n-th bulb in a corridor.
Output
Output “yes” or “no” to indicate if the light is on, or no !
So here is solution in Pascal :

Code:

program light;

uses wincrt;

var

n,i:integer;

a:array[1..10000] of boolean;

procedure fill_with_true;

var

  i:integer;

begin

  for i:=1 to 10000 do

  a[i]:=true;

end;

function check(k:integer):boolean;

var

  i,j:integer;

begin

  for i:=1 to k do

    for j:=1 to k do

      begin

        if j mod i = 0 then

          if a[i]=true then

            a[i]:=false

          else

            a[i]:=true;

      end;

    if a[k]=true then

      check:=true

    else

      check:=false;

end;

begin

writeln('enter n ');

readln(n);

fill_with_true;

if check(n) then

writeln('yes')

else

writeln('no');

end.