The Sum $$$\sum_{x=1}^{n}x^3$$$ has a closed form which is $$$(\frac{n(n+1)}{2})^2$$$

x=int(input())
print(x*(x+1)*x*(x+1)//4)

since the sum of numbers from $$$1$$$ to $$$n$$$ has a closed form $$$\frac{n(n+1)}{2}$$$ we can obtain the missing number by sum all the numbers from $$${1}$$$ to $$${n}$$$ (inclusive) and then sum the given numbers $$${x_1,x_2,x_3...,x_{n-1}}$$$ and find the difference so the final solution is $$$\frac{n(n+1)}{2}-\sum_{i=1}^{n-1}x_i$$$

n=int(input())
x=list(map(int,input().split()))
print(n*(n+1)//2-sum(x))

The Idea Here is Linearize the Time Complexity by using efficient popular algorithm called "Kadane's Algorithm" that maximize the sum in each iteration to get with the maximum subarray in $$$O(n)$$$ time complexity

n=int(input())
x=list(map(int,input().split()))
sm,best=0,0
for i in range(len(x)):
    sm=max(x[i],sm+x[i])
    best=max(best,sm)
print(best)

The Idea is to (string add) numbers even with themselves , so if we have n numbers then we will have $$$n*n=n^2$$$ (string add) operations that means that Time Complexity Here will Be $$$O(n^2)$$$ and of course in the iteration converting the string to integer and adding to the sum

n=int(input()) x=input().split() ar=[] for i in range(n): for j in range(n): ar.append(x[i]+x[j]) ar=list(map(int,ar)) print(sum(ar))