Memoization

Interval DP (choose the last step / merge equal ends), partition DP into k segments, palindrome tables plus partitioning, and memoizing the whole state when it is too tangled to split

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 2328 note: strictly increasing means no cycles; dp[cell] = 1 + Σ dp[larger neighbors], processed from largest to smallest value (or by memoized DFS), summed over all cells

LeetCode 488 note: with at most 16 balls on the board and 5 in hand, memoize DFS on the whole (board, hand) state, inserting only before a same-colored ball or between two equal balls

LeetCode 397 note: even numbers are always halved; for odd numbers try +1 and -1 with memoized recursion, since n is too large for an n-sized array

LeetCode 1137 note: like Fibonacci, roll three variables; watch the base values T0 = 0, T1 = T2 = 1 and the loop range

LeetCode 509 note: the starting point of 1D DP; only the previous two terms are needed, so roll two variables