Standard O(n^2) length-major DP for longest palindromic
subsequence:
dp[i][j] = dp[i+1][j-1] + 2 if s[i] = s[j]
= max(dp[i+1][j], dp[i][j-1]) otherwise
lps "BBABCBCAB" = 7 (witness "BABCBAB" etc.)
Complementary to manacher.ml (longest palindromic *substring*,
also length 7 on that input by coincidence) — this is the
subsequence variant which doesn't require contiguity.
Tests length-major fill order, inline if for the length-2 base
case, double-nested for with derived j = i + len - 1.
177 baseline programs total.
giles
f9371e7d22