adding concatenation of array, use 2 loops, or use the copy constructor

leetcode/l1929_concatenationofarray.cpp

@@ -0,0 +1,37 @@
+// basic approach: use two loops to generate the first half and the second half
+/*
+class Solution {
+public:
+    vector<int> getConcatenation(vector<int>& nums) {
+        // use the default constructor
+        vector<int> ans;
+        int size = nums.size();
+        for(int i=0;i<size;i++){
+            ans.push_back(nums[i]);
+        }
+        // do it one more time
+        for(int i=0;i<size;i++){
+            ans.push_back(nums[i]);
+        }
+
+        return ans;
+    }
+};
+*/
+
+// approach 2: use the copy constructor
+
+class Solution {
+public:
+    vector<int> getConcatenation(vector<int>& nums) {
+        // use the copy constructor
+        vector<int> ans(nums);
+        int size = nums.size();
+        // copy the second half
+        for(int i=0;i<size;i++){
+            ans.push_back(nums[i]);
+        }
+
+        return ans;
+    }
+};