LeetCode 486 Predict the Winner - Key Idea

Don't track two separate scores. Track the difference: $dp[i][j]$ = maximum (current player's score $-$ opponent's score) for subarray $[i, j]$.

Why difference? When I pick, I gain points. Then it's opponent's turn, and their "best difference" becomes my negative. The signs flip automatically. Player $1$ wins if $dp[0][n-1] \geq 0$: their advantage over the full array is non-negative. This single-number state avoids tracking both players' scores separately.