322. 零钱兑换

class Solution {
    public int coinChange(int[] coins, int amount) {
        int[]dp = new int[amount + 1];
        //不可能用到amount+1个硬币，所以用它初始化数组
        Arrays.fill(dp, amount + 1);
        dp[0] = 0;
        for(int i = 1; i <= amount; i++){
            for(int coin : coins)
                if (i - coin >= 0)
                    dp[i] = Math.min(dp[i], dp[i - coin] + 1);
        }

        //dp[amount]最开始被初始化为amount+1了，还为此值则代表无法变动
        if (dp[amount] == amount + 1) {
            dp[amount] = -1;
        }
        return dp[amount];
    }
}