First Duplicate

Author: ndstephens

14_First-Duplicate/index.js

@@ -0,0 +1,18 @@
+// First Duplicate
+// Write a function that takes in an array of positive numbers and returns the first number that is duplicated. If no duplicates occur, return -1.
+
+const firstDuplicate = numArr => {
+ const containerObj = {}
+
+ for (const num of numArr) {
+ if (containerObj[num]) {
+ return num
+ }
+ containerObj[num] = 1
+ }
+ return -1
+}
+
+console.log(firstDuplicate([2, 3, 3, 1, 5, 2]))
+console.log(firstDuplicate([2, 2]))
+console.log(firstDuplicate([2, 1, 3]))