# LeetCode – Combination Sum IV (Java)

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.

Java Solution

This problem is similar to Coin Change. It's a typical dynamic programming problem.

```public int combinationSum4(int[] nums, int target) { if(nums==null || nums.length==0) return 0;   int[] dp = new int[target+1];   dp[0]=1;   for(int i=0; i<=target; i++){ for(int num: nums){ if(i+num<=target){ dp[i+num]+=dp[i]; } } }   return dp[target]; }```
Category >> Algorithms
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• Ionut Mandra

‘if(i+num<=target)' shouldn't be: if (i + num <= target && i != num) ?
For nums [3,4,5,6] and target 9, when i = 3 and num =3 the algorithm would say:
dp[3+3] = dp[6] (=1 already from step i=0) + dp[3] (=1 already from step i=0)
but dp[6] it's not 2, you can't have 2 combinations of nums that will get you to 6, knowing that elements are unique.