reverse the order of words in a sentence

[noob.pas]

okay, i've been looking for a nice algorithm for this one for a long time, all i find are cpp, java and c# code. i've been trying to reverse the order of each word in its place, but i don't seem to be able to do so. i tried with two strings, swapping the chars of each word but it simply didn't work...
this is my...attempt to write each word backwards...

program stringzorz;

var
s1, s2 : string;
i, j ,k, start, endd : integer;

procedure swp(var c1, c2 : char);
          var p : char;
          begin
               p := c1;
               c1 := c2;
               c2 := p;
          end;

begin
     readln(s1);
     s2 := s1;
     endd := 1;
     i := 1;
     while i < length(s1) do
     begin
     while s1[i] <> ' ' do
           i:= i + 1;
     start := i;
     j := i;
     for i := endd to start do
         begin
              swp(s1[i], s2[j]);
              j := j - 1;
         end;
     end;
     writeln(s1);

end.

i know it's all...scrambled, i'm not that good at the esthetic part of coding but could someone please give me an idea atleast?

[noob.pas]

umm, the thread can be removed...or saved...i've found a better way of reversing a sentence by deleating :

program stringzorz;

var
s : string;
i, j, k : integer;

begin
     readln(s);
     insert(' ', s, 1);
     while length(s) > 1 do
           begin
                i := length(s);
                while s[i] <> ' ' do
                      i := i - 1;
                for j := i+1 to length(s) do
                    write(s[j]);
                delete(s, i + 1,  length(s) - i + 1);
                while s[i] = ' ' do
                      begin
                           if i = 1 then break;
                           write(s[i]);
                           i := i - 1;
                      end;
                delete(s, i + 1, length(s) - i + 1);
           end;
      readln;
end.

[Graham_Saint]

For what its worth, here is my solution:

VAR

s, t, w : string;
i : integer;

BEGIN

readln(s);
w := '';
t := '';


FOR i := 1 TO length(s) DO
  IF s[i] <> ' ' THEN
    w := w + s[i]
  ELSE IF length(w) > 0 THEN BEGIN
    t := w + ' ' + t;
    w := '';
  END;

IF length(w) > 0 THEN
  t := w + ' ' + t;

[Duoas]

If I had to do it in-place, I would have just reversed the entire string, then reversed each word in the string...

But you did a good job with your temp strings. Nice!

[Ranfile]

im facing the same problem like this. my boss like to know how to reverse word in a sentence but you can only use 1 byte buffer (byte or char). could you help me? TIA

if the input is i love you, it should be you love i. and the long of the string isnt defined...

[Duoas]

You'll need an index or pointer to the last character in the string, and an index or pointer to the first character in the string, and a temporary char. Then swap values, dec( last ), inc( first ) and repeat until last <= first.

Do the same thing for each word.

Good luck!

[Ranfile]

brilliant!!

thanks:)

but i would like to add that the last index/pointer need to find a space character before doing the swap proccess and then go back to an earlier word...:)

the rest would be the looping proccess:)

[Ranfile]

i found a simpler way to do it.. :)

like this :

input : im visiting your home
proccess : change the string upside down : emoh ruoy gnitisiv mi
do the 2nd process : turn it again by the words : home your visiting im

voila... we can do it with 1byte buffer much easier...

[Duoas]

Isn't that what I suggested in #4?

[Ranfile]

yes,absolutely:)

[Duoas]

Sorry I was grouchy. :$ :)

[Micheus]

Just another way to do this - introducing recursivity:

function Reverse(var value :string; start :integer) :string;
var
  StrTmp :string;
begin
  if start <= length(value) then
  begin
    StrTmp := '';
   // getting the word
    while (start <= length(value)) and
          (value[start] <> ' ') do
    begin
      StrTmp := StrTmp +value[start];
      Inc(start);
    end;
  // preserve spaces and put it before the word
    while value[start] = ' ' do
    begin
      StrTmp := ' ' +StrTmp;
      Inc(start);
    end;
  // recursive call to get the next word and insert it before the actual - StrTmp
    Reverse := Reverse(value, start) +StrTmp;
  end else
    ReverseWord := '';
end;

var
  sl :string;
begin
  readln(sl);
  sl := Reverse(sl, 1);
  writeln(sl);
end.

Bye

[tylcoatc]

var St,StReverse:String; m,n:Integer;
begin
  St:='I need to reverse this sentence';
  StReverse:='';
  n:=Length(St)+1;
  repeat
    m:=n;
    repeat dec(n); until (St[n]=' ') or (n=0);
    StReverse:=StReverse+' '+Copy(St,n+1,m-n-1);
  until n=0;
  Label1.Caption:=St+':'+StReverse;
end;

You can get the input string/strings from anywhere.
This was simply to show you another way!