LeetCode 1140 Stone Game II - Walkthrough

Piles: $[2, 7, 9, 4, 4]$. Player can take first $1$ to $2M$ piles. $M$ starts at 1, updates to $\max(M, X)$ after taking $X$ piles. $dp[i][M]$ = max stones current player can get from piles $[i:]$ with parameter $M$. From $dp[0][1]$: can take 1 pile (get 2) or 2 piles (get 9).

After taking $X$, opponent gets $dp[i+X][\max(M,X)]$, I get the rest. observation: I get $suffixSum[i] - dp[i+X][\max(M,X)]$. The opponent's best becomes my loss. Find the largest over valid $X$.