HDU 1016 Prime Ring Problem(深搜+回溯+剪枝+Eratosthenes素数筛)
PrimeRingProblemAringiscomposeofncirclesasshownindiagram.Putnaturalnumber1,2,…,nintoeachcircleseparately,andthesumofnumbersintwoadjacentcirclesshouldbeaprime.Note:thenumberoffirstcircleshouldalwaysbe1