Sum it up 题意:给定一个数sum,和n个数,求sum可以由这n个数里面的那几个数的和表示. Given a specified total t and a list of n integers, find all distinct sums using numbers from the list that add up to t. For example, if t=4, n=6, and the list is [4,3,2,2,1,1], then there are four d…