Simple C# solution
Approach\n- Notice that the most optimal way to obtain the minimum possible sum using 4 digits is by summing up two 2-digit numbers.\n- We can use the two small
# Approach\n- Notice that the most optimal way to obtain the minimum possible sum using 4 digits is by summing up two 2-digit numbers.\n- We can use the two smallest digits out of the four as the digits found in the tens place respectively.\n- Similarly, we use the final 2 larger digits as the digits found in the ones place.\n\n# Complexity\n- Time complexity: $$O(1)$$\n- Space complexity: $$O(1)$$\n\n# Code\n```\npublic class Solution\n{\n    public int MinimumSum(int num)\n    {\n        var sortedDigits = num.ToString().OrderBy(x => x).Select(x => x - \'0\').ToArray();\n        var num1 = sortedDigits[0] * 10 + sortedDigits[2];\n        var num2 = sortedDigits[1] * 10 + sortedDigits[3];\n\n        return num1 + num2;\n    }\n}\n```
['C#']