Combination Sum IV

Java

class Solution {
    public int combinationSum4(int[] nums, int target) {
        if(nums == null || target == 0) return 0;
        
        int [] dp = new int [target + 1];
        dp[0] = 1;
        
        for(int i = 1; i <= target; i ++){
            for(int j = 0; j < nums.length; j ++){
                if(i - nums[j] >= 0){
                    dp[i] += dp[i - nums[j]];
                }
            }
        }
        return dp[target];
    }
}