Given an integer array stock_prices where stock_prices[i] represents the price of a stock on day i, compute the maximum profit achievable by performing at most two buy-sell transactions. You cannot hold more than one stock at a time (i.e., you must sell before buying again). Return the maximum possible profit as an integer.
Example 1
Input: [2, 4, 1, 7, 5, 3, 6]
Output: 10
Explanation: Buy at 1, sell at 7 (profit 6). Buy at 3, sell at 6 (profit 3). Total profit: 6+3=9. But buying at 2, selling at 4 (profit 2), then buying at 1, selling at 7 (profit 6) gives 2+6=8. Best is buy at 1, sell at 7 (profit 6), buy at 3, sell at 6 (profit 3), total 9.
Example 2
Input: [8, 1, 2, 10, 4, 9]
Output: 14
Explanation: Buy at 1, sell at 10 (profit 9). Buy at 4, sell at 9 (profit 5). Total profit: 9+5=14.
Example 3
Input: [5, 4, 3, 2, 1]
Output: 0
Explanation: No profitable transaction possible.
Constraints
Case 1
Input: [1, 5, 2, 8, 3, 7]
Expected: 11
Case 2
Input: [10, 9, 8, 7, 6, 5]
Expected: 0
Case 3
Input: [3, 2, 6, 5, 0, 3]
Expected: 7
Case 4
Input: [1, 2, 4, 2, 5, 7, 2, 4, 9, 0]
Expected: 13