I wrote a code for linear search in python(recursive). Can somebody tell me why it isn't workin-CodePudding

lister=[4,5,1,2,3,6]

i=0
def Search(arr):
    if arr[i]==3:
        return i
    else:
        if i>=0 and i<=(len(arr)-2):          
            i 1
            return Search(arr)
        else:
            return -1

print(Search(lister))

Linear Search using recursion in python.

I don't know why its not working.

CodePudding user response：

There are 2 main issues.
The first is that you're not incrementing i anywhere. i 1 doesn't modify i, just returns the value of i 1 which you're not placing anywhere. To increment i you should use i = 1.
The second is you're not using the externally defined i variable in your Search function.

To fix this you could either declare it as global in the start of your method, or pass it as a parameter to your function.

Global method (less preferable):

lister=[4,5,1,2,3,6]

i=0
def Search(arr):
    global i
    if arr[i]==3:
        return i
    else:
        if i>=0 and i<=(len(arr)-2):          
            i =1
            return Search(arr)
        else:
            return -1

print(Search(lister))

And the parameter method (which would be preferable):

lister=[4,5,1,2,3,6]

def Search(arr, i=0):
    if arr[i]==3:
        return i
    else:
        if i>=0 and i<=(len(arr)-2):          
            i =1
            return Search(arr, i)
        else:
            return -1

print(Search(lister))

CodePudding user response：

You are not incrementing i variable. You have i 1 but you don't assign it to i. You should have i=i 1 or i =1 for short. This recursive call function is looping infinitely, since i doesn't change.

CodePudding user response：

Rather than explicitly testing that the index is in range, why not use exception handling? You can also manage the any potential recursion "overflow" in this manner. For example:

def rfind(_list, val, idx=0):
    try:
        if _list[idx] == val:
            return idx
        return rfind(_list, val, idx 1)
    except (IndexError, RecursionError):
        return -1


print(rfind([1, 2, 3], 2))
print(rfind([1, 2, 3], 4)) # will return None due to IndexError
print(rfind([], 4)) # will return None due to IndexError
print(rfind([0]*2000, 1)) # will return None due to RecursionError

Output:

1
-1
-1
-1