Question

In python, write a function, called ThreeSum, that accepts a list of non-negative numbers as input, and returns the highest sum of three neighboring elements in it. Write a main method that initializes the following five lists, gets the ThreeSum result for all of them using the above function, and prints the result to the screen. Example of the output: List 1: [4,5,4,5] , Three sum = 14 List 2: [7] , Three sum = 7 List 3: [ ] , Three sum = 0 List 4: [8,1] , Three sum = 9 List 5: [1,3,5,7,4,2,9] , Three sum = 16

Answer 1

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Steps:

1. Define a function threesum
2. Define a functio main
3. In three sum do , the following steps from 4 till 7
4. Find the largest value and its position
5. if length of the list is less than or equal to 3 then add all the elements in the list   
6. if length of list is greater than 3 add, the max value, and the 2 values near to the max values .
7. if list is empty , return sum as zero.
8. print the result sum from main

Source Code(# comments are given)(screen shot of code is given after the code, refer it for indentation checking)

#function threesum with argument as list_1

def threeSum(list_1):

#max will store the threesums of all the list

#large will store the largest element in each list
max=[]
large=0

#n contains the length of list passed
n=len(list_1)

#checking conditions
if n<3:
sum=0
for i in list_1:
sum+=i
return sum
elif n<1:
sum=0
return sum
else:
for item in range(n-2):
pos=0
sum=0
if pos==0:
sum=list_1[item]
pos+=1
if pos==1:
sum+=list_1[item+1]
pos+=1
if pos==2:
sum+=list_1[item+2]
pos+=1
max.append(sum)
for l in max:
if l>large:
large=l
return large

#main function to call threeSum and print the sum

def main():
list1=[4,5,4,5]
list2=[7]
list3=[]
list4=[8,1]
list5=[1,3,5,7,4,2,9]
print(list1)
sum=threeSum(list1)
print("ThreeSum = "+str(sum))
print(list2)
sum=threeSum(list2)
print("ThreeSum = "+str(sum))
print(list3)
sum=threeSum(list3)
print("ThreeSum = "+str(sum))
print(list4)
sum=threeSum(list4)
print("ThreeSum = "+str(sum))
sum=threeSum(list5)
print(list5)
print("ThreeSum = "+str(sum))

main()

Screenshot of code

Screenshot of output