Not the fastest solution, but as a newbie, I found this an easy way to practice recursion

```
public class Solution {
public int recurse(int[] nums, int i) {
if(i <= 1) return nums[0];
return Math.min(nums[i],nums[i-1]) + recurse(nums,i-2);
}
public int arrayPairSum(int[] nums) {
if(nums.length == 2) return nums[0];
Arrays.sort(nums);
return recurse(nums, nums.length-1);
}
}
```