Question

I need to write a function that takes a list and bisects it (like the bisect module but I cannot use that). I normally would show what I have done so far but I really do not know how to do it without the module so I am hoping someone can help me out a bit. Here is the exact question I need to figure out:

Write a function called bisect that takes a sorted list and a target value and returns the index of the value in the list, if it’s there, or None if it’s not

Answer 1

The bisect module keeps track of a list, keeping it sorted, without having to resort every time you insert an element. The method you need to implement just needs to search inside a sorted list.

def bisect(sortedlist,targetvalue,firstindex=0,lastindex=None):

    if(len(sortedlist)==0):
        return None
    if(len(sortedlist)==1):
        if(sortedlist[0]==targetvalue):
            return firstindex
        else:
            return None
    center = int(round(len(sortedlist)/2))

    if(sortedlist[center]==targetvalue):
        return firstindex+center
    if(targetvalue>sortedlist[center]):
        return bisect(sortedlist[center+1:lastindex],targetvalue,center+1,lastindex)
    else:
        return bisect(sortedlist[0:center],targetvalue,firstindex,center-1)

this basically does a binary search.
The indexes are passed to keep track of the indexes of the original list, in invocations further down the recursion loop.