# Find the first repeated element in an array by its index

**Objective:** Given an array of integers, find out the first repeated element. First repeated element means the element occurs atleast twice and has smallest index.

**Input:** An Array

**Output: **The first repeated element

**Examples** :

Array {1,1,3,4,6,7,9} first repeated Number : 1 Array {7,2,2,3,7} first repeated Number : 7 Array {5,3,3,3,3,3,3,3,4,4,4,5,3} first repeated Number : 5

**Approach: **

**Naive Solution :**

Use two for loops. Time Complexity O(N^{2}).

**Better Solution: Using HastSet, Time Complexity O(N).**

- Take a variable say
*index = -1.* - Initialize a HashSet.
- Navigate the array from right to left(backwards) taking one element at a time
- if HashSet doesnt contain element, add it
- if HashSet contains then update the index with current index in navigation.
- At the end index will be updated by the element which is repeated and has the lowest index.

**Complete Code:**

**Output:**

{1,2,5,7,5,3,10,2} first repeated element by index is : 2