Solution.java

// github.com/RodneyShag

import java.util.Scanner;
import java.util.HashMap;

// Main trick: Use a HashMap<Integer, Integer> that maps from "value" to "index" 
//             to keep track of the largest index for each value that we've 
//             seen so far as we loop through array

//  Time Complexity: O(n)
// Space Complexity: O(n)

// Complete the minimumDistances function below.
static int minimumDistances(int[] array) {
    HashMap<Integer, Integer> map = new HashMap();
    int minDistance = Integer.MAX_VALUE;
    for (int i = 0; i < array.length; i++) {
        if (map.containsKey(array[i])) {
            int prevIndex = map.get(array[i]);
            int currDistance = i - prevIndex;
            minDistance = Math.min(minDistance, currDistance);
        }
        map.put(array[i], i);
    }
    return minDistance == Integer.MAX_VALUE ? -1 : minDistance;
}

// Discuss on HackerRank: https://www.hackerrank.com/challenges/minimum-distances/forum/comments/360084