题目：

题解：

func combinationSum4(nums []int, target int) int {
    dp := make([]int, target+1)
    dp[0] = 1
    for i := 1; i <= target; i++ {
        for _, num := range nums {
            if num <= i {
                dp[i] += dp[i-num]
            }
        }
    }
    return dp[target]
}