Lessons from Edit Distance

Four things to remember:

$1.$ String DP compares prefixes. $dp[i][j]$ relates prefix of A to prefix of $B$.

$2.$ Match vs operate. When characters match, you get a free transition.

$3.$ Three choices become one min. Replace, delete, insert map to three neighbors.

$4.$ Base cases are edge strings. Empty-to-something costs the length. You now have three 2D patterns: resource tracking, grid navigation, and string comparison.