17/11/20
SELECTION SORT
Example:
A: <5, 2, 4, 6, 1, 3>
Index 1 2 3 4 5 6
A 5 2 4 6 1 3
We change 1 with 5 because 1 is the min.
1, 2, 4, 6, 5, 3
You always scam all the list and then you exchange the value. Then you compare 2 with all the values
and at the last index you have 4<3? False, so 3 is the new min, and you change it with 4.
1, 2, 3, 6, 5, 4
3 is the new min so you compare 6 with all the elements and at the last index you have 6<4? False, so you
change it with 4 and you have: 1, 2, 3, 4, 5, 6
The complexity is quadratic because in the worst case you have 6^6.
In terms of asymptotic running time selection sort and insertion sort are the same.
Basically selection sort doesn’t make any difference between the worst case and all the other cases,
whereas insertion sort is linear except for the worst case.
SELECTION-SORT(A)
n = len(A)
for j = 1 to n-1 do
minimum= j
for i = j + 1 to n do
if (A[i] < A[min]) then
minimum = i
exchange A[j] with A[minimum]
When you reach n-1 the number n is sorted by definition that’s why you go on until n-1 and not until n. In
pseudocode and python you don’t have to specify the update (j = j+1), because in the for loop is implicit
in the to, so every time you start again the for, j is automatically updated. In the second iteration it would
be j = 2 and then you start again. When you see multiple loops nested inside one other the complexity is
quadratic.
24/11/20
FILE SYSTEM
WHAT’S A FILE?
A file is a contiguous logical address space. This means that it is a sequence of bytes in our hard drive
that is logical contiguous. This is the formal definition.
A file is defined by its type:
1) Data: numeric, character, binary;
2) Program (phyton code)
The contents are defined by file’s creator: we have many types (text files, source files, executable files).
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