def selection_sort(L): Pre: L is a list of numbers Post: L is sorted in non-decreasing order II III # i indicates how many items were sorted for i in range (len(L)): # To find the minimum value of the unsorted segment # We first assume that the first element is the lowest min_index = i # We then use j to loop through the remaining elements for j in range (i+1, len(L)): # Update the min_index if the element at j is lower than it if L[j] < L[min_index]: min_index j # After finding the lowest item of the unsorted regions, # swap with the first unsorted item L[i], L[min_index] L [min_index], L[i] %3D The loop invariant for the outer loop is rather simple: 0 < i < len(L) and L[0 : i] is sorted. Clearly, once the loop finishes and i = len(L), this implies the postcondi- tion, and L is sorted. State and prove the loop invariant for the inner loop that can be used to prove the loop invariant for the outer loop. However, you do not need to prove how it is connected to the outer loop (though this is good practice). Hint: You should start by fixing a value for i, and assuming the outer loop in- variant holds for that i. You should use this assumption in your proof for the inner loop invariant.

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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def selection_sort(L):
II III|
Pre: L is a list of numbers
Post: L is sorted in non-decreasing order
II IIII
# i indicates how many items were sorted
for i in range(len(L)):
# To find the minimum value of the unsorted segment
# We first assume that the first element is the lowest
min_index
= i
# We then use j to loop through the remaining elements
for j in range (i+1, len(L)):
# Update the min_index if the element at
if L[j] < L[min_index]:
is lower than it
min_index
%3D
# After finding the lowest item of the unsorted regions,
# swap with the first unsorted item
L[i], L[min_index]
L [min_index], L[i]
%3D
The loop invariant for the outer loop is rather simple: 0 <i< len(L) and L[0 : i]
is sorted. Clearly, once the loop finishes and i = len(L), this implies the postcondi-
tion, and L is sorted.
State and prove the loop invariant for the inner loop that can be used
to prove the loop invariant for the outer loop. However, you do not need to
prove how it is connected to the outer loop (though this is good practice).
Hint: You should start by fixing a value for i, and assuming the outer loop in-
variant holds for that i. You should use this assumption in your proof for the inner
loop invariant.
Transcribed Image Text:def selection_sort(L): II III| Pre: L is a list of numbers Post: L is sorted in non-decreasing order II IIII # i indicates how many items were sorted for i in range(len(L)): # To find the minimum value of the unsorted segment # We first assume that the first element is the lowest min_index = i # We then use j to loop through the remaining elements for j in range (i+1, len(L)): # Update the min_index if the element at if L[j] < L[min_index]: is lower than it min_index %3D # After finding the lowest item of the unsorted regions, # swap with the first unsorted item L[i], L[min_index] L [min_index], L[i] %3D The loop invariant for the outer loop is rather simple: 0 <i< len(L) and L[0 : i] is sorted. Clearly, once the loop finishes and i = len(L), this implies the postcondi- tion, and L is sorted. State and prove the loop invariant for the inner loop that can be used to prove the loop invariant for the outer loop. However, you do not need to prove how it is connected to the outer loop (though this is good practice). Hint: You should start by fixing a value for i, and assuming the outer loop in- variant holds for that i. You should use this assumption in your proof for the inner loop invariant.
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