# File:    recurSumLists.py
# Author:  Dr. Gibson
# Date:    11/10/2017
# Section: N/A
# E-mail:  k.gibson@umbc.edu
# Description:
#   This file contains python code that has multiple
#   implementations of a recursive "list summer" function

####################################################################
# recSumList1() sums a list by adding the first element to the rest
#               of the list recursively
# Input:        currList; a list of integers
# Output:       total of the list's contents
def recSumList1(currList):

    # BASE CASE: list is empty, nothing more to sum together
    if len(currList) == 0:
        return 0

    # RECURSIVE CASE: list is not empty, keep going
    else:
        # helps trace what's going on, but not necessary
        print("Adding", currList[0], "to", currList[1:] )

        # RECURSIVE CALL: add first element to sum of rest of list
        return currList[0] + recSumList1( currList[ 1: ] )

##################################################################
# recSumList2() sums a list by keeping track of what index
#               we're at when adding the entire list together
# Input:        theList; a list of integers
#               currIndex; index of contents to be added in next
# Output:       total of the list's contents
def recSumList2(theList, currIndex):

    # BASE CASE: reached the end of the list, stop adding
    if currIndex == len(theList):
        return 0

    # RECURSIVE CASE: not at the end of the list, keep going
    else:
        # helps trace what's going on, but not necessary
        print("Now adding", theList[currIndex], "at index", currIndex)
        # RECURSIVE CALL: add current element, call on next one
        return theList[currIndex] + recSumList2(theList, currIndex + 1)
        



def main():

    myList = [3, 5, 8, 7, 2, 6, 1]

    print("\tAdding the list", myList, "together:")
    ans1 = recSumList1(myList)
    print("The sum of the list is", ans1)


    print("\n\tAdding a different way: ")
    # requires that we give starting index, so start at position 0
    ans2 = recSumList2(myList, 0)
    print("The sum of the list is", ans2)



main()