Practice list algorithms — reverse, remove duplicates, and find minimum
Implement reversing a list without using the built-in reverse() method.
Remove duplicate values from a list while preserving order — no set() allowed.
Find the smallest number in a list without using the built-in min() function.
Compute the sum 1 + 2 + ... + (n-1) using sigma notation — e.g. n=10 returns 45.