Quicksorter V2
20
The best programmers I’ve meet knew how to sort a deck of cards pretty d*mn well Tony Tran
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Transcript of Quicksorter V2
The b
est
pro
gra
mm
ers
I’ve m
eet
knew
how
to
sort
a d
eck o
f card
s
pre
tty d
*mn
well
Tony T
ran
Sto
ry T
ime ☺
Ima
ge
so
urc
e:
http
://w
ww
.eye
bro
wm
aga
zin
e.c
om
/__da
ta/a
sse
ts/im
age
/001
0/1
00
45
/me
gan_
fox_na
ked_5
.jp
g
Wh
at
if
•G
iven
:D
eck o
f pla
yin
g c
ard
s
•G
oal:
To r
etr
ieve a
ny c
ard
as fast as
possib
le!
•C
on
str
ain
ts:
No
real constr
ain
ts,
do w
ha
tever
you
want
with the
card
s! Ju
st
do
n’t
be a
sm
art
@s*!
WH
AT
WO
UL
D Y
OU
DO
!?!
Fin
d m
e:
Appro
aches:
1. D
o n
oth
ing to the d
eck (
Cost: 5
2 lookups)
Co
st
is a
naly
zed
in
wo
rst
case s
cen
ari
o.
"An
yth
ing t
hat
can g
o w
rong w
ill g
o w
ron
g.“
–M
urp
hy’s
La
w
Appro
aches:
1.
Do n
oth
ing t
o t
he d
eck (
Cost:
52 lookups)
2.
Gro
up c
ard
s b
y s
uits (
Cost:
4+
12 =
16 looku
ps)
3.
Gro
up c
ard
s b
y f
aces (
Cost:
12+
4 =
16 lookups)
Image s
ourc
e:
htt
p:/
/ww
w.f
lickr.
com
/photo
s/6
0601
862@
N00
/94247
611
6/
Wh
at
if
•G
iven
:99 n
ote
card
s w
ith a
uniq
ue
num
ber
written o
n e
ach c
ard
.
•G
oal:
To r
etr
ieve a
ny c
ard
as fast as
possib
le!
•C
on
str
ain
ts:
No
real constr
ain
ts,
do w
ha
tever
you
want
with the
card
s! Ju
st
do
n’t
be a
sm
art
@s*!
WH
AT
WO
UL
D Y
OU
DO
!?!
Fin
d m
e:
Appro
aches:
1.
Do n
oth
ing to the d
eck (
Cost: 9
9 lookups)
2.
Cre
ate
bin
s for
gro
ups o
f 100 a
nd just th
row
the c
ard
s into
the b
in.
Exam
ple
:
Co
st
is a
naly
zed
in
wo
rst
case s
cen
ari
o.
"An
yth
ing t
hat
can g
o w
rong w
ill g
o w
ron
g.“
–M
urp
hy’s
La
w
bin
s
(Cost:
99 looku
ps)
When g
ive
n c
ard
s:
1,2
,3,D
,99
Fin
d m
e:
Appro
aches:
1.
Do n
oth
ing to the d
eck (
Cost: 9
9 lookups)
2.
Cre
ate
bin
s for
gro
ups o
f 100 a
nd just th
row
the c
ard
s into
the b
in. (C
ost: 9
9 lookups)
3.
So
rt t
he
de
ck!
Th
en
pe
rfo
rm b
ina
ry s
ea
rch
to
fin
d
ca
rd.
(co
st:
lo
g2(9
9)
loo
ku
ps ~
= 7
lo
ok u
ps)
Co
st
is a
naly
zed
in
wo
rst
case s
cen
ari
o.
"An
yth
ing t
hat
can g
o w
rong w
ill g
o w
ron
g.“
–M
urp
hy’s
La
w
Dep
ictio
n o
f b
ina
ry s
earc
h (
do
es n
ot
sho
w e
ntire
sea
rch
)
Fin
d m
e:
Appro
aches:
1.
Do n
oth
ing to the d
eck (
Cost: 9
9 lookups)
2.
Cre
ate
bin
s for
gro
ups o
f 100 a
nd just th
row
the c
ard
s into
the b
in. (C
ost: 9
9 lookups)
3.
So
rt t
he
de
ck!
Th
en
pe
rfo
rm b
ina
ry s
ea
rch
to
fin
d
ca
rd.
(co
st:
lo
g2(9
9)
loo
ku
ps ~
= 7
lo
ok u
ps)
Co
st
is a
naly
zed
in
wo
rst
case s
cen
ari
o.
"An
yth
ing t
hat
can g
o w
rong w
ill g
o w
ron
g.“
–M
urp
hy’s
La
w
Dep
ictio
n o
f b
ina
ry s
earc
h (
do
es n
ot
sho
w e
ntire
sea
rch
)
☺
Ho
w d
oes t
his
apply
to
pro
gra
mm
ing
?Abstraction!
Key p
oin
t #1 a
nd #
2:
1. B
ein
g a
ble
to a
bstr
act
a p
roble
m to
som
eth
ing less c
om
ple
x, or
more
fam
ilia
r,
will
make the p
roble
m e
asie
r!
Ima
ge
so
urc
e:
http
://w
ww
.scie
ntifica
me
rica
n.c
om
/med
ia/in
line
/3E
0F
91
60
-E7
F2
-99
DF
-35899
8A
A3
C1
A91
0F
_1
.jpg
2. A
bstr
acting a
pro
ble
m to a
pro
ble
m that
has a
lready b
een s
olv
ed is e
ven b
etter!
You d
on’t r
eally
have to d
o a
ny w
ork
!
•“t
he
pu
rpo
se
of
abstr
actio
n is notto
be
va
gu
e,
bu
t to
cre
ate
a n
ew
se
ma
ntic le
ve
l in
wh
ich
on
e
ca
n b
e a
bso
lute
ly p
recis
e.”
-E
dsg
er
W.
Dijk
str
a
Oth
er
fans o
f abstr
action
What
is t
he s
hort
est
path
fro
m 1
to a
ny o
ther
node
?
“[O
SP
F] com
pute
s t
he s
hort
est
path
tre
e f
or
each r
oute
usin
g a
meth
od b
ased o
n D
ijkstr
a's
alg
orith
m,
a s
hort
est
path
first
alg
ori
thm
.”
INT
ER
NE
T!!
!
Keypoin
t#3
3.
Th
ere
’s n
o s
uch t
hin
g a
s a
du
mb
pro
ble
m
Ima
ge
so
urc
e:
http
://s
fist.
co
m/a
tta
chm
en
ts/S
Fis
t_B
rock/p
an
ca
ke
s.jpg
Pro
ble
m:
Giv
en a
spatu
la a
nd a
dis
h o
f pan
cakes (
sa
y 6
for
no
w),
ho
w w
ould
yo
u f
lip t
he p
an
cakes s
uch t
ha
t th
e p
ancakes b
ecom
e s
ort
ed
with t
he larg
est
pancake
at
the b
ott
om
and s
malle
st
at
the t
op? H
ow
man
y s
teps w
ould
it
requ
ire?
FL
IP
Init
ial S
tate
:G
OA
L
Som
eone fa
mili
ar:
•B
ill G
ate
s&
Christo
s P
apadim
itriou,
Bounds F
or
Sort
ing B
y P
refix R
evers
al.
Discrete Mathematics, vol27, pp 4
7-5
7,
1979.
We r
efe
rred t
o b
oun
ds a
s “
Co
sts
”
SO
RT
ING
PA
NC
AK
ES
==
SO
RT
ING
BY
PR
EF
IX R
EV
ER
SA
L
Key P
oin
ts:
1. B
ein
g a
ble
to a
bstr
act
a p
roble
m to s
om
eth
ing less c
om
ple
x, or
more
fam
iliar,
will
make the p
roble
m e
asie
r!
2. A
bstr
acting a
pro
ble
m to a
pro
ble
m that has a
lre
ady b
een s
olv
ed is
even b
etter!
3. T
here
’s n
o s
uch thin
g a
s a
dum
b p
roble
m.
4. B
e c
rea
tive
an
d h
av
e f
un
wit
h p
rob
lem
s.
Yo
u h
ave
th
e a
bilit
y t
o c
reate
an
en
tire
wo
rld
at
yo
ur
fin
ge
rtip
s!
The b
est
pro
gra
mm
ers
I’ve m
eet
kne
w h
ow
to A
BS
TR
AC
T P
RO
BLE
MS
pre
tty d
*mn
we
ll
“The h
ard
est
part
of
solv
ing a
pro
ble
m is t
o c
om
ple
tely
und
ers
tand it
to
a p
oin
t w
here
you c
an s
ee it
from
man
y d
iffe
rent
pers
pective
s a
nd a
bstr
actions”
-A v
ery
wis
e T
.A.
-TH
AN
K Y
OU
-
New
tit
le p
rop
osal:
P.S
. M
y g
fw
ill p
rob
ab
ly b
e r
ead
ing
th
is,
so
th
e s
tory
at
the b
eg
inn
ing
did
n’t
reall
y h
ap
pen
0-=
) B
ut
reall
y,
it d
idn
’t ☺ ☺☺☺
Thank y
ou,
-Tony T
ran
@quic
ksort
er
