Create 1346. Check If N and Its Double Exist (#648)

Author: Chayandas07

1346. Check If N and Its Double Exist

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+class Solution {
+public:
+    bool checkIfExist(vector<int>& arr) {
+        int n = arr.size();
+        bool cnt[2001] = {false}; // Boolean array to track whether a number has been seen
+
+        for(int i = 0 ; i < n ; i++) {
+            int x = arr[i] * 2 + 1000;
+            if(x >= 0 && x <= 2000 && cnt[x]) //Check if 2 * arr[i] exists and not exceed the range
+                return true; 
+            x = arr[i] / 2 + 1000;
+            if(arr[i] % 2 == 0 && cnt[x]) //ensure arr[i] is even and check if arr[i] / 2 exists
+                return true; 
+            cnt[arr[i] + 1000] = 1;
+        }
+        return false;
+    }
+};