Add Solution.java for 0349.Intersection of Two Arrays

Author: huaxu1024

solution/0349.Intersection of Two Arrays/README_EN.md

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+# Intersection of Two Arrays
+
+Given two arrays, write a function to compute their intersection.
+
+## Example 1:
+```
+Input: nums1 = [1,2,2,1], nums2 = [2,2]
+Output: [2]
+```
+
+## Example 2:
+```
+Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4]
+Output: [9,4]
+```
+Note:
+
+* Each element in the result must be unique.
+* The result can be in any order.

solution/0349.Intersection of Two Arrays/Solution.java

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+class Solution {
+    public int[] intersection(int[] nums1, int[] nums2) {
+        HashSet<Integer> set1 = new HashSet<Integer>();
+        for (Integer n : nums1) set1.add(n);
+        HashSet<Integer> set2 = new HashSet<Integer>();
+        for (Integer n : nums2) set2.add(n);
+
+        set1.retainAll(set2);
+
+        int [] output = new int[set1.size()];
+        int idx = 0;
+        for (int s : set1) output[idx++] = s;
+        return output;
+    }
+}