[C++ Dynamic Programming Enhancement] Add multiple knapsack & brute force/memo solutions

[Phoenix8215]

This Pull Request enhances the dynamic programming section of the C++ code in the “hello algo” project by adding new examples and approaches:

• Unbounded Knapsack (Complete Knapsack)
  Added brute force (recursive) solution and memoized solution to show top-down approaches alongside the existing bottom-up DP.

• Multiple Knapsack Problem
  Introduced a new complete code example for the multiple knapsack problem, illustrating how it differs from the 0/1 and unbounded knapsack problems.

• Coin Change Problem
  Added brute force and memoized (top-down) solutions, so readers can compare different strategies (recursive vs. DP) for the same problem.

[krahets]

Hi @Phoenix8215,

We do not plan to provide brute force and memo code for this section.