题目：

题解：

class Solution {public int change(int amount, int[] coins) {int[] dp = new int[amount + 1];boolean[] valid = new boolean[amount + 1];dp[0] = 1;valid[0] = true;for (int coin : coins) {for (int i = coin; i <= amount; i++) {valid[i] |= valid[i - coin];}}if(!valid[amount]) return 0;for (int coin : coins) {for (int i = coin; i <= amount; i++) {dp[i] += dp[i - coin];}}return dp[amount];}
}