nearly 100% in runtime in C#
\n\n# Code\n\npublic class Solution {\n    public int[] GetConcatenation(int[] nums) {\n        var result = new int[nums.Length * 2];\n        for (int i = 0; 
\n\n# Code\n```\npublic class Solution {\n    public int[] GetConcatenation(int[] nums) {\n        var result = new int[nums.Length * 2];\n        for (int i = 0; i < nums.Length; i++)\n        {\n            result[i] = nums[i];\n            result[i+nums.Length] = nums[i];\n        }\n        return result;\n    }\n}\n```
['C#']