firstRepeatingEle.cpp

// Given an array arr[] of size n, find the first repeating element. The element should occurs more than once and the index of its first occurrence should be the smallest.
//
//
//
// Example 1:
//
// Input:
// n = 7
// arr[] = {1, 5, 3, 4, 3, 5, 6}
// Output: 2
// Explanation:
// 5 is appearing twice and
// its first appearence is at index 2
// which is less than 3 whose first
// occuring index is 3.






class Solution {
  public:
    // Function to return the position of the first repeating element.
    int firstRepeated(int arr[], int n) {
        unordered_map<int,int> mpp;
        for(int i=0;i<n;i++)
        {
            mpp[arr[i]]++;
        }
        for(int i=0;i<n;i++)
        {
            if(mpp[arr[i]] >= 2)
            {
                return i+1;
            }
        }
        return -1;
    }
};