回溯法求解子集和数给定一个n个整数的集合X={x1,x2....xn}和整数y,找出和等于y的X的子集Y.

The backtracking method solves the subset and the number given a set of n integers X={x1,x2....xn} and the integer y, finds a subset Y of the X equal to and equal to y.