Combination Sum 4

Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target.

Example:

nums = [1, 2, 3]
target = 4

The possible combination ways are:
(1, 1, 1, 1)
(1, 1, 2)
(1, 2, 1)
(1, 3)
(2, 1, 1)
(2, 2)
(3, 1)

Note that different sequences are counted as different combinations.

Therefore the output is 7.

Solution

public class Solution {
    public int combinationSum4(int[] nums, int target) {
        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];
    }
}