feat: added 217-Contains-Duplicate solution

Author: diego.junges.ter

javascript/217-Contains-Duplicate.js

@@ -0,0 +1,13 @@
+class Solution {
+  containsDuplicate(nums) {
+    const hashmap = new Set()
+    for (let num of nums) {
+      if (hashmap.has(num)) {
+        return true
+      } else {
+        hashmap.add(num)
+      }
+    }
+    return false
+  };
+}