Sum of Multiplication of each number with sum of other numbers of an array in rotational manner-CodePudding

Example:

Input : [4 3 5 1]
Output: 118

Explanation:

4*(3 5 1)=>36
3*(4 5 1)=>30
5*(4 3 1)=>40
1*(4 3 1)=>12
Therefore, (36 30 40 12=)118

What would be the code to implement it?

CodePudding user response：

You can use sum with generator comprehension:

lst = [4, 3, 5, 1]

output = sum(x * (sum(lst) - x) for x in lst)
print(output) # 118

If there the list is long, then you might want to pre-calculate sum(lst) and store it in a separate variable.

CodePudding user response：

You can obtain that result by subtracting the sum of squares from the square of the sum:

a = [4,3,5,1]

sum(a)**2 - sum(n**2 for n in a)  # 118