dp[l][r] = string with minimal size that contains s[l...r] as subsequence.

dp[l][r] = min{ dp[l][i] + dp[i + 1][r] | l <= i < r }
dp[l][r] = min(dp[l][r], s[l] + dp[l + 1][r — 1] + s[r]) if s[l] = '(' and s[r] = ')' (or '[', ']')

Plus means concatination, min means string with mininal length.