Selection Sort, For Java

问题

I am having trouble understanding this pseudocode, and implementing it into my program. Can anybody explain it better or show me how the code would look? Thanks.

A - an array containing the list of numbers
numItems - the number of numbers in the list

for i = 0 to numItems - 1
    for  j = i+1 to numItems               
        if A[i] > A[j]
            // Swap the entries
            Temp = A[i]
            A[i] = A[j]
            A[j] = Temp          
        End If    
    Next j
Next i

回答1:

Well, let's translate the pseudo-code to pseudo-English.

A - an array containing the list of numbers
numItems - the number of numbers in the list

for i = 0 to numItems - 1
    for  j = i+1 to numItems               
        if A[i] > A[j]
            // Swap the entries
            Temp = A[i]
            A[i] = A[j]
            A[j] = Temp          
        End If    
    Next j
Next i

which might read

Count through each item, from the beginning to the end, calling it X
  While considering item X, count through each item after it, from just
  after X to the end, calling it Y
    If X is bigger than Y, swap the two, temporarily storing X in Temp
      so it doesn't get lost when we copy Y into X.  Copy Y into X, and then
      Copy the temporarily stored old value of X (remember it is in Temp)
      back into Y.  Now the values of X and Y are swapped (so X is now smaller
      than Y)

Now it's your job to write it in code.

回答2:

The name of the algorithm tells you a whole lot about it. It first selects the smallest element of the list and puts it in the first spot. Then it selects the second and puts it in the second, etc.

How do you find the smallest element? Well you look through the list, and if the element you're looking at is smaller than the element at the beginning of the list, swap it in.

How do you find the second smallest? You know that the smallest element is already in the first spot. So that means the second smallest must be the smallest element between the second element and the end of the list. So you go through and do the appropriate swaps again.

Lather, rinse, and repeat.

If you're wondering how elements are swapped. Just think about how you would do it by hand. You pick element 1 up and put it in a safe place, put element 2 in element 1's old spot, then put element 1 in element 2's old spot. The temporary variable used would represent the safe place you put element 1.

Wikipedia has a nice article on it.

回答3:

If all you want to do is sort an array of ints into a specific order and your professor doesn't mind you using a utility class then Go Here.

However, if you are required to write the sorting algorithm yourself then Go Here there are explanations and examples.

来源：https://stackoverflow.com/questions/10852522/selection-sort-for-java

标签

java

pseudocode