Suppose that we want to build a trinary code for the 26 letters of the alphabet, using strings in which each symbol is 0, 1, or ; 1. (a) Could we encode all 26 letters using strings of length at most 2? Answer this question by enumeration.

Letter	Code
a	-1
b	0
c	1
d	-1-1
e	-10
f	-11
g	0-1
h	00
i	01
j	1-1
k	10
l	11 (the last possible code)
m
n
o
p
q
r
s
t
u
w
v
x
y
z

so the answer is NO

2. What about using strings of length exactly 3?

Letter	Code
a	-1-1-1
b	-1-10
c	-1-11
d	-10-1
e	-100
f	-101
g	-11-1
h	-110
i	-111
j	0-1-1
k	0-10
l	0-11
m	00-1
n	000
o	001
p	01-1
q	010
r	011
s	1-1-1
t	1-10
u	1-11
w	10-1
v	100
x	101
y	11-1
z	110

so the answer is YES