Dynamic-Programming

Prefix tables, edit operations, subsequences, and interval palindrome DP

0/1, unbounded, reachability, counting, and optimization states

Counting, cost optimization, reverse resource DP, and local geometry

LeetCode 940 note: group by last character; distinct subsequences ending with c = every current distinct subsequence with c appended, plus c itself, replacing the old value

LeetCode 2973 note: the max product of three is either the three largest or the two smallest times the largest, so each subtree returns only its 2 smallest and 3 largest values, merged in post-order

LeetCode 1246 note: interval DP taking the minimum of removing arr[i] alone, removing equal ends together with the inside, or splitting into two parts

LeetCode 1425 note: dp[i] = nums[i] + max(0, max of the previous k dp values); that max is a sliding window maximum, available in O(1) from a monotonic deque

LeetCode 1373 note: a post-order traversal returns (sum, min, max, is_bst); a node roots a BST when the left max < its value < the right min

LeetCode 996 note: with n at most 12, use bitmask DP: dp[mask][last] = permutations using the set mask and ending with last; dedupe by using equal values in index order

LeetCode 773 note: there are only 6! = 720 boards, so flatten each board into a string as a BFS state, with swaps of 0 and a neighbor as the moves

LeetCode 2376 note: digit DP with state (pos, tight, started, mask); the mask records used digits, and leading zeros must not mark 0 as used

LeetCode 2163 note: try every boundary k between the two parts; the left takes the n smallest of nums[:k] (a max-heap) and the right the n largest of nums[k:] (a min-heap), one prefix and one suffix pass