feat: Add solution for concatenation-of-array problem

easy/concatenation-of-array.test.ts

@@ -0,0 +1,12 @@
+// Problem: https://leetcode.com/problems/concatenation-of-array/
+// Doc: https://leetcode.com/problems/concatenation-of-array/solutions/5472607/double-your-array-fun-with-concatenation/
+const getConcatenation = (nums: number[]): number[] => [...nums, ...nums];
+
+describe('Concatenation of Array', () => {
+  it('should return the concatenated array', () => {
+    expect(getConcatenation([1])).toEqual([1, 1]);
+    expect(getConcatenation([1, 1])).toEqual([1, 1, 1, 1]);
+    expect(getConcatenation([1, 2, 1])).toEqual([1, 2, 1, 1, 2, 1]);
+    expect(getConcatenation([1, 3, 2, 1])).toEqual([1, 3, 2, 1, 1, 3, 2, 1]);
+  });
+});