
Theoretical Computer Science Cheat Sheet
Denitions Series
f
(
n
)=
O
(
g
(
n
)) i
9
positive
c n
0
such that
0
f
(
n
)
cg
(
n
)
8
n
n
0
.
n
X
i
=1
i
=
n
(
n
+1)
2
n
X
i
=1
i
2
=
n
(
n
+1)(2
n
+1)
6
n
X
i
=1
i
3
=
n
2
(
n
+1)
2
4
:
In general:
n
X
i
=1
i
m
=
1
m
+1
(
n
+1)
m
+1
;
1
;
n
X
i
=1
;
(
i
+1)
m
+1
;
i
m
+1
;
(
m
+1)
i
m
n
;
1
X
i
=1
i
m
=
1
m
+1
m
X
k
=0
m
+1
k
B
k
n
m
+1
;
k
:
Geometric series:
n
X
i
=0
c
i
=
c
n
+1
;
1
c
;
1
c
6
=1
1
X
i
=0
c
i
=
1
1
;
c
1
X
i
=1
c
i
=
c
1
;
c
c<
1
n
X
i
=0
ic
i
=
nc
n
+2
;
(
n
+1)
c
n
+1
+
c
(
c
;
1)
2
c
6
=1
1
X
i
=0
ic
i
=
c
(1
;
c
)
2
c<
1
:
Harmonic series:
H
n
=
n
X
i
=1
1
i
n
X
i
=1
iH
i
=
n
(
n
+1)
2
H
n
;
n
(
n
;
1)
4
:
n
X
i
=1
H
i
=(
n
+1)
H
n
;
n
n
X
i
=1
i
m
H
i
=
n
+1
m
+1
H
n
+1
;
1
m
+1
:
f
(
n
)=(
g
(
n
)) i
9
positive
c n
0
such that
f
(
n
)
cg
(
n
)
0
8
n
n
0
.
f
(
n
)=(
g
(
n
)) i
f
(
n
) =
O
(
g
(
n
)) and
f
(
n
)=(
g
(
n
)).
f
(
n
)=
o
(
g
(
n
)) i lim
n
!1
f
(
n
)
=g
(
n
)=0.
lim
n
!1
a
n
=
a
i
8
2
R
,
9
n
0
such that
j
a
n
;
a
j
<
,
8
n
n
0
.
sup
S
least
b
2
R
such that
b
s
,
8
s
2
S
.
inf
S
greatest
b
2
R
such that
b
s
,
8
s
2
S
.
lim inf
n
!1
a
n
lim
n
!1
inf
f
a
i
j
i
n i
2
N
g
.
lim sup
n
!1
a
n
lim
n
!1
sup
f
a
i
j
i
n i
2
N
g
.
;
n
k
Combinations: Size
k
sub-
sets of a size
n
set.
n
k
Stirling numbers (1st kind):
Arrangements of an
n
ele-
mentsetinto
k
cycles.
1.
n
k
=
n
!
(
n
;
k
)!
k
!
2.
n
X
k
=0
n
k
=2
n
3.
n
k
=
n
n
;
k
4.
n
k
=
n
k
n
;
1
k
;
1
5.
n
k
=
n
;
1
k
+
n
;
1
k
;
1
6.
n
m
m
k
=
n
k
n
;
k
m
;
k
7.
X
k
n
r
+
k
k
=
r
+
n
+1
n
8.
n
X
k
=0
k
m
=
n
+1
m
+1
9.
n
X
k
=0
r
k
s
n
;
k
=
r
+
s
n
10.
n
k
=(
;
1)
k
k
;
n
;
1
k
11.
n
1
=
n
n
=1
12.
n
2
=2
n
;
1
;
1
13.
n
k
=
k
n
;
1
k
+
n
;
1
k
;
1
n
k
Stirling numbers (2nd kind):
Partitions of an
n
element
set into
k
non-emptysets.
n
k
1st order Eulerian numbers:
Permutations
1
2
:::
n
on
f
1
2
:::n
g
with
k
ascents.
n
k
2nd order Eulerian numbers.
C
n
Catlan Numbers: Binary
trees with
n
+1 vertices.
14.
n
1
=(
n
;
1)!
15.
n
2
=(
n
;
1)!
H
n
;
1
16.
n
n
=1
17.
n
k
n
k
18.
n
k
=(
n
;
1)
n
;
1
k
+
n
;
1
k
;
1
19.
n
n
;
1
=
n
n
;
1
=
n
2
20.
n
X
k
=0
n
k
=
n
!
21.
C
n
=
1
n
+1
2
n
n
22.
n
0
=
n
n
;
1
=1
23.
n
k
=
n
n
;
1
;
k
24.
n
k
=(
k
+1)
n
;
1
k
+(
n
;
k
)
n
;
1
k
;
1
25.
0
k
=
n
1 if
k
=0,
0 otherwise
26.
n
1
=2
n
;
n
;
1
27.
n
2
=3
n
;
(
n
+1)2
n
+
n
+1
2
28.
x
n
=
n
X
k
=0
n
k
x
+
k
n
29.
n
m
=
m
X
k
=0
n
+1
k
(
m
+1
;
k
)
n
(
;
1)
k
30.
m
!
n
m
=
n
X
k
=0
n
k
k
n
;
m
31.
n
m
=
n
X
k
=0
n
k
n
;
k
m
(
;
1)
n
;
k
;
m
k
!
32.
n
0
=1
33.
n
n
=0 for
n
6
=0
34.
n
k
=(
k
+1)
n
;
1
k
+(2
n
;
1
;
k
)
n
;
1
k
;
1
35.
n
X
k
=0
n
k
=
(2
n
)
n
2
n
36.
x
x
;
n
=
n
X
k
=0
n
k
x
+
n
;
1
;
k
2
n
37.
n
+1
m
+1
=
X
k
n
k
k
m
=
n
X
k
=0
k
m
(
m
+1)
n
;
k