Sort Integers by the Power Value (Collatz)

Question

## Problem

Sort integers in [lo, hi] by their Collatz-style 'power' (steps to reach 1), ties by value; return the k-th.

## Example
```
lo=12, hi=15, k=2 -> 13
```

## Constraints
- 1 ≤ lo ≤ hi ≤ 1000

## Approach
Compute power with memoization; sort by (power, value). Reported IBM OA question.