1582 articles
LC 97 Interleaving String asks whether s3 can be formed by interleaving s1 and s2 while preserving character order. The 2D DP table dp[i][j] checks whether s3[:i+j] can be formed from s1[:i] and s2[:j] — a classic Boolean 2D DP problem asked at Google and Amazon.
LC 10 Regular Expression Matching implements "." (any char) and "*" (zero or more of preceding) using 2D DP. It is a Hard-level problem and the most complex string DP asked at Google and Meta — the star (*) handling requires 3 separate cases that trip up even experienced candidates.
LeetCode 44 Wildcard Matching is the classic 2D string DP question Meta and Google ask to test recurrence design under tricky base cases. We derive the dp[i][j] transitions for ? and *, dry-run a full table, and finish with a two-pointer optimization that drops memory to O(1).
LeetCode 174 Dungeon Game is the textbook example of why DP direction matters. We derive why forward DP fails, build the backward dp[i][j] = max(1, ...) recurrence, dry-run the grid, and finish with a space-optimized 1D solution loved at FAANG.
LeetCode 474 Ones and Zeroes is the cleanest two-capacity 0/1 knapsack on the platform. We derive the dp[i][j] recurrence, walk a full 2D table, and ship a 1D-collapsed solution that handles the dual-resource constraint while staying interview-friendly.