Christmas is coming soon and you still have so many things to buy. You are going to the store and don't expect to spend more than X dollars. You want to be able to pay any integer amount not exceeding X dollars, and you want to take as few coins as possible to achieve this.
You are given a int values, each element of which describes the dollar value of a kind of coin. You have an unlimited supply of each kind of coin. Return the minimal number of coins you need to take, or -1 if it is impossible to achieve your goal.