.model small
.stack
.data
crlf db 0Dh, 0Ah, '$'
str1 db 30 dup(0), '$'
str2 db 30,0,30 dup(0)
counter dw 0

.code
start:
mov ax,@data
mov ds,ax
mov es,ax

lea si,str2+2
lea di,str1

mov ah,0Ah
lea dx,str2
int 21h

lea dx,crlf
mov ah,9
int 21h

mov cx,30
xor ax,ax
mov dx,di

let:
lodsb
cmp al,0dh
je if1
cmp al,0
je exit
cmp al,' '
je if1
inc counter
stosb
loop let
jmp exit

if1:
mov bx,si
mov si,dx
mov di,dx
xor cx,cx
mov cx,counter
mov ah,cl
while:
lodsb
stosb
repne scasb
cmp cx,0
ja clear
mov cx,counter
sub di,cx
dec counter
loop while
mov counter,0
mov al,' '
stosb
mov si,bx
mov dx,di
jmp let

clear:
mov di,dx
mov al,0
mov cl,ah
rep stosb
mov counter,0
mov di,dx
mov si,bx
mov dx,di
jmp let

exit:
lea dx,str1
mov ah,9h
int 21h

mov ah,4ch
int 21h

end start