Sorting: Selection Sort Damian Gordon. Sorting: Selection Sort OK, so we’ve seen a way of sorting that easy for the computer, now let’s look at a ways.

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Presentation transcript:

Sorting: Selection Sort Damian Gordon

Sorting: Selection Sort OK, so we’ve seen a way of sorting that easy for the computer, now let’s look at a ways that’s more natural for a person to understand. It’s called SELECTION SORT.

Sorting: Selection Sort It works as follows: – Find the smallest number, swap it with the value in the first location of the array – Find the second smallest number, swap it with the value in the second location of the array – Find the third smallest number, swap it with the value in the third location of the array – Etc.

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort

Sorting: Selection Sort So we know we only have to swap if the value is not already in the correct location.

Sorting: Selection Sort So we know we only have to swap if the value is not already in the correct location. This will look a little something like this:

Sorting: Selection Sort So we know we only have to swap if the value is not already in the correct location. This will look a little something like this: IF (MinValueLocation != CurrentLocation) THEN Swap(Age[CurrentLocation], Age[MinValueLocation]; ENDIF;

We will find the minimum value in the list using something like the following: MinValueLocation <- 0; FOR Index IN IncreasingCount TO N-1 DO IF (Age[Index] < Age[MinValueLocation]) THEN MinValueLocation <- Index; ENDIF; ENDFOR; Sorting: Selection Sort

So we can put these two bits together,

PROGRAM SelectionSort: Integer Age[8] <- {44,23,42,33,16,54,34,18}; FOR Outer-Index IN 0 TO N-1 MinValueLocation <- Outer-Index; FOR Index IN Outer-Index+1 TO N-1 DO IF (Age[Index] < Age[MinValueLocation]) THEN MinValueLocation <- Index; ENDIF; ENDFOR; IF (MinValueLocation != Outer-Index) THEN Swap(Age[Outer-Index], Age[MinValueLocation]); ENDIF; ENDFOR; END. Sorting: Selection Sort

etc.