Add Solution.java to problems 1346

Author: huaxu1024

solution/1346. Check If N and Its Double Exist/README_EN.md

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+# Check If N and Its Double Exist
+
+Given an array arr of integers, check if there exists two integers N and M such that N is the double of M ( i.e. N = 2 * M).
+
+More formally check if there exists two indices i and j such that :
+* i != j
+* 0 <= i, j < arr.length
+* arr[i] == 2 * arr[j]
+
+## Example 1:
+```
+    Input: arr = [10,2,5,3]
+    Output: true
+    Explanation: N = 10 is the double of M = 5,that is, 10 = 2 * 5.
+ 
+```
+
+## Example 2:
+```
+    Input: arr = [7,1,14,11]
+    Output: true
+    Explanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.
+
+```
+
+## Example 3:
+```
+    Input: arr = [3,1,7,11]
+    Output: false
+    Explanation: In this case does not exist N and M, such that N = 2 * M.
+    
+```
+
+
+## Constraints:
+   * 2 <= arr.length <= 500
+   * -10^3 <= arr[i] <= 10^3

solution/1346. Check If N and Its Double Exist/Solution.java

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+import java.util.*;
+
+class Solution {
+    public boolean checkIfExist(int[] arr) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int i = 0; i < arr.length; i++) {
+            map.put(arr[i], i);
+        }
+        for (int i = 0; i < arr.length; i++) {
+            if (map.containsKey(arr[i] * 2) && i != map.get(arr[i] * 2))
+                return true;
+        }
+        return false;
+    }
+}