feat: solve contains-duplicate

Author: GangBean

contains-duplicate/GangBean.java

@@ -0,0 +1,12 @@
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        /***
+            compare length of array and length of set.
+            O(n) given that n is length of array nums
+        */
+        return nums.length > Arrays.stream(nums).boxed().collect(Collectors.toSet()).size();
+    }
+}