518.零钱兑换Ⅱ。完全背包

完全背包问题，从前往后

class Solution {
    public int change(int amount, int[] coins) {
        int[] dp = new int[amount + 1];
        dp[0] = 1;
        for(int i = 0; i < coins.length; i++){
            for(int j = 1; j <= amount; j++){
                if(j >= coins[i]) dp[j] += dp[j - coins[i]];
            }
        }
        return dp[amount];
    }
}