Question

PYTHON- create recursive functions for these examples. has to be recursive with base cases and cannot have loops!

- Return sum of all the #'s inside a certain list. list should not be empty

-if a list contains a certain target return True , False otherwise

- if two strings contain exactly the same chars that are in the same order return True, False otherwise

- if "pre" is a prefix for a string "str", return true and false otherwise

Answer 1

Here is the code for all the four functions usig recursion.

#Example-1
#recursive functin returns sum of elemetns in the passed list parameter
def sum_of_elements(mylist):
    # if list is empty , return the 0 value
    if(mylist == []):
        return 0
    #get first item from list
    item = mylist[0]
    #update the list , by slicing (removing first item)
    mylist = mylist[1:]
    # recursive call by removing first element and add it with rest of the list's sum
    return(item + sum_of_elements(mylist))
    
    
    
#Example-2
#this function returns true, if target is found in the list , otuherwise returns false
def find_target(mylist,target):
    #if list becomes empty, it means no target found.
    if(mylist==[]):
        return False
    #pop an item from list,if it is target, return true 
    item = mylist[0]
    mylist = mylist[1:] 
    if(target==item):
        return True
    #if poped element is not target, call recursively for rest of the list
    else:
        return find_target(mylist,target)
        
        
        
#Example-3
#this funciton compare string by each index recursively
def compare(s1, s2):
    # base condition, if both strign becomes empty, return true
    if(s1 == "" and s2 == ""):
        return True
    # if both strings has different lengths,they can;t be same.
    if(len(s1) != len(s2)):
        return False
    # if poped elements are same, then call function recursively for rest lists to compare
    if(s1[0] == s2[0]):
        return compare(s1[1:], s2[1:])

    # if none of the case, return false
    return False


#Example-4
#this function checks that, if first argument is a prefix for second argument or not.
def checkPrefix(prefix,mystring):
    #if pre string becomes empyt, return true
    if(prefix==""):
        return True
        #if mystring is shorter than pre,it mean pre can;t be prefix of mystring 
    if(mystring=="" and prefix!=""):
        return False
    #if first indexes, matches of both strings, we call recursively for rest strings
    if(prefix[0]==mystring[0]):
        return checkPrefix(prefix[1:],mystring[1:])
    return False
    
    
#testing all funcitons
a = sum_of_elements([1,2,3,-2,4]) #answer should be 8
b = find_target([1,2,6,5,4],6)    #answer should be True
c = compare("Nikhil","Nikhik")    #anser should be False
d = checkPrefix("nik",'nikfg')    #anser should be True
#print all funcitons answers
print(a,b,c,d)

.

output:

Hope It Helps!

Thumbsup ;)