First Repeating Element

Task: Find the first repeating element in given an array of N elements. If it is present then print that index else print -1.

Example:

Input:

1

1 2 2 3 1

Output:

1 

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Here is the Code:

Program in C++:

1. #include<iostream>
2. #include<bits/stdc++.h>
3. using namespace std;
4. int main()
5.  {
6. int t;
7. cin>>t;
8. while(t--)
9. {
10.     int n;
11.     cin>>n;
12.     int a[n];
13.     unordered_map<int, int> m;
14.     for(int i=0;i<n;i++)
15.     {
16.         cin>>a[i];
17.         m[a[i]]++;
18.     }
19.     int c=0;
20.     for(int i=0;i<n;i++)
21.     {
22.         if(m[a[i]]>1)
23.         {
24.             cout<<i+1<<endl;
25.             c=1;
26.             break;
27.         }
28.     }
29.     if(c==0) cout<<-1<<endl;
30. }
31. return 0;
32. }

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Here is the Video: