func change(amount int, coins []int) int {
	res := make([]int, amount+1)
	// res[j] amount = j 有多少种方式
	res[0] = 1
	for i := 0; i < len(coins); i++ { // 物品在外层
		for j := coins[i]; j <= amount; j++ { // 容量在里层
			res[j] += res[j-coins[i]]
		}
		//log.Println(res)
	}

	return res[amount]
}

func combinationSum4(nums []int, target int) int {
	res := make([]int, target+1)
	res[0] = 1
	for j := 0; j <= target; j++ { // 背包容量在外层
		for i := 0; i < len(nums); i++ { // 物品在里层
			if j-nums[i] >= 0 {
				res[j] += res[j-nums[i]]
			}
		}
		//log.Println(res)
	}

	return res[target]
}