2605. Form Smallest Number From Two Digit Arrays

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2605. Form Smallest Number From Two Digit Arrays

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Given two arrays of unique digits nums1 and nums2, return the smallest number that contains at least one digit from each array.
 

Example 1:

Input: nums1 = [4,1,3], nums2 = [5,7]
Output: 15
Explanation: The number 15 contains the digit 1 from nums1 and the digit 5 from nums2. It can be proven that 15 is the smallest number we can have.
Example 2:

Input: nums1 = [3,5,2,6], nums2 = [3,1,7]
Output: 3
Explanation: The number 3 contains the digit 3 which exists in both arrays.
 

Constraints:

1 <= nums1.length, nums2.length <= 9
1 <= nums1[i], nums2[i] <= 9
All digits in each array are unique.

Difficulty : Easy

Solution

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class Solution {
    public int minNumber(int[] nums1, int[] nums2) {
        TreeSet<Integer> s1 = toSet(nums1);
        TreeSet<Integer> s2 = toSet(nums2);
        int a = s1.first();
        int b = s2.first();
        s1.retainAll(s2);
        if (!s1.isEmpty()) {
            //have to create new TreeSet, otherwise will get exception
            return new TreeSet<>(s1).first();
        }
        return Math.min(a, b) * 10 + Math.max(a, b);

    }

    public static TreeSet<Integer> toSet(int[] nums) {
        return Arrays.stream(nums).boxed().collect(Collectors.toCollection(TreeSet::new));
    }    
}