projecteuler---->problem=31----Coin sums 无限背包计算可能存在的次数
Problem31InEnglandthecurrencyismadeupofpound,£,andpence,p,andthereareeightcoinsingeneralcirculation:1p,2p,5p,10p,20p,50p,£1(100p)and£2(200p).Itispossibletomake£2inthefollowingway:1×£1+1×50p+2×20p+1×5p