LeetCode 474 Ones and Zeroes - Two Capacities

Define $dp[i][j]$ = max strings selectable using at most $i$ zeros and $j$ ones. Your answer is $dp[m][n]$. For each string with $z$ zeros and $o$ ones, the formula is: $dp[i][j] = \max(dp[i][j], dp[i-z][j-o] + 1)$.

Process each string and update the 2D (two-dimensional) DP array backwards (from $m$ down to $z$, from $n$ down to $o$) to avoid reusing the same string. It's the same backwards-loop trick from 0/1 knapsack, just in two dimensions.