Minimum Sum of Four Digit Number After Splitting Digits

Problem

You are given a positive integer num consisting of exactly four digits. Split num into two new integers new1 and new2 by using the digits found in num. Leading zeros are allowed in new1 and new2, and all the digits found in num must be used.

For example, given num = 2932, you have the following digits: two 2's, one 9 and one 3. Some of the possible pairs [new1, new2] are [22, 93], [23, 92], [223, 9] and [2, 329].

Return **the *minimum* possible sum of new1 and **new2.

Example 1:

Input: num = 2932
Output: 52
Explanation: Some possible pairs [new1, new2] are [29, 23], [223, 9], etc.
The minimum sum can be obtained by the pair [29, 23]: 29 + 23 = 52.

Example 2:

Input: num = 4009
Output: 13
Explanation: Some possible pairs [new1, new2] are [0, 49], [490, 0], etc. 
The minimum sum can be obtained by the pair [4, 9]: 4 + 9 = 13.

Constraints:

1000 <= num <= 9999

Solution (Java)

class Solution {
    public int minimumSum(int num) {
        int[] digit = new int[4];
        int cur = 0;
        while (num > 0) {
            digit[cur++] = num % 10;
            num /= 10;
        }
        Arrays.sort(digit);
        int num1 = digit[0] * 10 + digit[2];
        int num2 = digit[1] * 10 + digit[3];
        return num1 + num2;
    }
}

Explain:

nope.

Complexity:

Time complexity : O(n).
Space complexity : O(n).