农夫过河问题讲述的是一位农夫带着一只狼，一只羊和一颗白菜要渡过一条河，只有农夫能开船，且每次农夫只能带最多一样东西，并且农夫不在的时候，狼和羊，羊和白菜不能共存，我们需要在这个前提下找到渡河的最短路径。(About the farmer across the river is a farmer with a wolf, a sheep and a cabbage to cross a river, the farmer can only sail, and each farmer can only take up something, and when the farmer is not the wolf and sheep, sheep and cabbage can not coexist, the shortest path we need find the river on the premise of the)