Maximum distance between two occurrences of same element in array

http://www.geeksforgeeks.org/maximum-distance-two-occurrences-element-array/
An efficient solution for this problem is to use hashing. The idea is to traverse input array and store index of first occurrence in a hash map. For every other occurrence, find the difference between index and the first index stored in hash map. If difference is more than result so far, then update the result.

int maxDistance(int arr[], int n)

{

    // Used to store element to first index mapping

    unordered_map<int, int> mp;

 

    // Traverse elements and find maximum distance between

    // same occurrences with the help of map.

    int max_dist = 0;

    for (int i=0; i<n; i++)

    {

        // If this is first occurrence of element, insert its

        // index in map

        if (mp.find(arr[i]) == mp.end())

            mp[arr[i]] = i;

 

        // Else update max distance

        else

            max_dist = max(max_dist, i - mp[arr[i]]);

    }

 

    return max_dist;

}