Solve shipping capacity and expression insertion

Problem A: Minimum shipping capacity

You are given an array weights where weights[i] is the weight of the i-th package. Packages must be shipped in order (you cannot reorder). You have D days to ship all packages.

Each day, you load a contiguous prefix of the remaining packages onto the ship, up to the ship's capacity C. The total weight loaded that day cannot exceed C.

Task: Return the minimum integer capacity C that allows shipping all packages within D days.

Input:

• weights : array of positive integers
• D : positive integer

Output:

• Minimum feasible ship capacity C

Example:

• weights = [1,2,3,4,5,6,7,8,9,10] , D = 5 → output 15

Constraints (typical):

• 1 <= len(weights) <= 1e5
• 1 <= weights[i] <= 1e5
• 1 <= D <= len(weights)

Problem B: Insert +, -, or concatenate to hit target

You are given a string s consisting only of digits (e.g., "123") and an integer target.

You may insert between any two adjacent digits one of:

• '+'
• '-'
• nothing (concatenate digits into a multi-digit number)

This forms an arithmetic expression evaluated left-to-right with normal integer addition/subtraction.

Task: Return all distinct expressions (as strings) that evaluate to target.

Rules / edge cases:

• A number token cannot have leading zeros (e.g., "05" is invalid), except the token "0" itself.
• You must use the digits in s in order; you cannot reorder or skip digits.

Input:

• s : digit string
• target : integer

Output:

• List of expression strings that evaluate to target (order not important)

Example:

• s = "123" , target = 6 → ["1+2+3"]
• s = "105" , target = 5 → ["10-5"] (but not "1+0+5" if it doesn't match)

Constraints (typical):

• 1 <= len(s) <= 10~12 (small enough to allow backtracking)
• Result count may be large; return all that exist