CODEWITHSUNDEEP
pythonrecursionselection-sort
Chicacchironi
Chicacchironi

Reputation: 35

How to return value of number of swaps in Selection Sort recursive in python

The Code:

def selection(list, i, j, flag, swapNumber):
    
    size = len(list)
    if (i < size - 1):
        if (flag):
            j = i + 1;
            print(list)
            
        if (j < size):
            if (list[i] > list[j]):
              swapNumber +=1
              print(swapNumber)
              list[i],list[j]=list[j],list[i]
            
            print(list)
            selection(list, i, j + 1, 0, swapNumber);
            
        
        else:
            selection(list, i + 1, i+2, 1, swapNumber);
    return(swapNumber)       


      
swapNumber = 0
list = [6, 2, 3, 7, 1]
numSwap = selection(list, 0, 1, 1, swapNumber)
print(list)
print(numSwap)

So I'm trying to return the value of the swapNumber but when it prints it just says 1. I tried placing the return(swapNumber) somewhere else didn't seem to help. Anyone can help with this?

Upvotes: 0

Views: 133

Answers (2)

go2nirvana
go2nirvana

Reputation: 1648

One cheecky way would be to define a function inside of a function and use nonlocal. Would look like this:

def selection_sort(list_):
    swaps = 0
    def selection(list_, i, j, flag):
        nonlocal swaps
        size = len(list_)
        if i < size - 1:
            if flag:
                j = i + 1

            if j < size:
                if list_[i] > list_[j]:
                    swaps += 1
                    list_[i], list_[j] = list_[j], list_[i]

                selection(list_, i, j + 1, 0)
            else:
                selection(list_, i + 1, i + 2, 1)
        return swaps
    return selection(_list, 0, 1, 1)

The benefit is also the fact that you don't need to pass 0, 1, 1 as initial params, just the list to be sorted itself.

Upvotes: 1

heLomaN
heLomaN

Reputation: 1804

The swapNumber passed to function selection is by value other than by reference.

One possible solution is declare it to be global:

def selection(list, i, j, flag):
    global swapNumber
    size = len(list)
    if (i < size - 1):
        if (flag):
            j = i + 1;
            print(list)
            
        if (j < size):
            if (list[i] > list[j]):
              swapNumber +=1
              print(swapNumber)
              list[i],list[j]=list[j],list[i]
            
            print(list)
            swapNumber = selection(list, i, j + 1, 0);
            
        
        else:
            swapNumber = selection(list, i + 1, i+2, 1);
    return(swapNumber)       


      
swapNumber = 0
list = [6, 2, 3, 7, 1]
numSwap = selection(list, 0, 1, 1)
print(list)
print(numSwap)

Upvotes: 1

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