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DSA complete summary
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All material from weeks 1 to 6 of DSA for econometrics students
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esraa al-obaydiinsertionsort -(f bounds
for j = 2 to n do TIN) =
(f (N) iff E c
,
no >O S t . .
O MI Ro ,
T(n) <C .
f(n)
current = A [j] ; T(n) = (f(N)) iff 7 <, no >O S t .
.
O MERo ,
T(N) < c .
F(N
i =
j
-
1 ; T(N) = 0 (f(n)) iff 74 , ,
2020 S .
t .
O R = No
,
4 .
f(n) [T(n) EG .
f(n)
while i <O and A [i] > current do
A [i + ] A [i] correctness of algorithms
=
i 1 1j by induction
=
-
of iterations i
end 7) IH >
-
a loop invariant condition ,
in terms
A [i + 1] = current ; 2) base case
end 3) inductive step
4) conclusion
comparison Cased current8 previous element to
algorithm >
compares
- -
determine their correct position in the sorted list example proof Insertionsort Literative algorithms)
1) the start of j-1]
IH : at iteration j ,
the
subarray A [1 : is sorted
worst case in order 2) base case show that at the start of iteration j the
array reverse 2
: : =
,
↳ 0(n2) A [1]
subarray is
trivially sorted by def
3) inductive
best case
array is
already sorted step show that each iteration of the loop maintains
: :
↳ -(n) the loop invariant
↳ intuition :
for iteration j ,
the while loop in the
runtime
algorithm body of the loop sequentially moves
every
T(N = an + 2(n 1) + (s(n 1) + cu& E tj + Cs
S 2(tj=
-
1) + element A [j-1] , Alj-2] , one element to the
(2(tj -
1) + 20(n- )
right ,
until A[j] can be inserted ,
hence
before the next iteration of the loop ,
A
[ij]
best case: T(n) = (2 + (2 + (3 + (4 + (0) .
n -
(2 + (3 + (4 + (0) is sorted
4) induction
=
a .
n -
b :
by induction, we conclude that the loop invariant holds
for all
J .
specifically at the last check for
divide 8 conquer N+ )
algorithm the loop condition (I = which proves that the
7) divide : break the
given problem into sulproblems of the same
array is sorted .
type
2) Conquer :
recursively solve these sueproblems , if suproblem example proof Mergesort
is small
enough ,
solve
directly 7) IH : In
every recursive call on an
array with
length <i algorithm ,
3) Combine combine the returns sorted
:
appropiatly answers
array
2) base step :
for E ,
the IH holds ,
since A is sorted
3)
Merge Sort induction :
take
any K with In, assume holds o
arrays of size ick
show that
based on divide & conquer 6(n loga (n) we have to IH holds for i = k
,
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