LeetCode 1140 Stone Game II - State Design

$dp[i][M]$ = maximum stones the current player can collect from piles $[i, n-1]$ when the parameter is $M$. Base case: if $i \geq n$, no piles left, return $0$.

If $i + 2M \geq n$, current player takes all remaining piles. Transition: try taking $X$ piles for $X = 1$ to $2M$. Stones I get = suffix$[i]$ $-$ suffix$[i + X]$. Then opponent plays from $i + X$ with $M' = \max(M, X)$. My total = stones taken $+$ (remaining $-$ opponent's best).