Two extreme hypotheticals that came up while I was discussing Dominion with the guy who first introduced me to it.
1. Optimal strategy or algorithm for a green-only kingdom. No other restrictions. Go.
There are (off the top of my head) 11 green kingdom cards, resulting in 11 possible kingdoms: Duke, Fairgrounds, Farmland, Gardens, Great Hall, Harem, Island, Nobles, Silk Road, Tunnel, Vineyard. Therefore, one of these clearly needs to be removed. IMO, the most likely candidates would seem to be Tunnel (for doing nothing) or Vineyard (for technically adding Potion to the game).
2. Optimal strategy for a yellow-only kingdom. No other restrictions. Go.
Bank, Cache, Contraband, Fool's Gold, Harem, Hoard, Horn of Plenty, Ill-Gotten Gains, Loan, Philosopher's Stone, Quarry, Royal Seal, Stash, Talisman, Venture. 15 cards, resulting in 3,003 possible kingdoms. For this, it seems to make sense to remove the not-so-functional Quarry, but 5 would need to be pulled. It would seem Cache, Hoard, Quarry, and Stash would be the least interesting to keep while Contraband and IGG would seem to have the most impact.