import java.util.Scanner;
import java.util.Stack;
import java.util.*;
 
class Ideone {
    public static void main(String[] args) {
        int[] inp = {1,2,3,1, 2, 1, 3};
        Map<Integer, Integer> h = new HashMap<>();
        List<Integer> result = new ArrayList<>();
        for (int i = inp.length - 1; i >= 0; --i) {
            int cur = inp[i];
            int next = -1;
            if (h.containsKey(cur)) {
                next = h.get(cur);
            }   
            h.put(cur, i);
            result.add(next);
        }
 
        for (int i = 0; i < inp.length; ++i) {
            System.out.println("Number " + inp[i] + " next occurence at index " + result.get(inp.length - i - 1));
        }
    }
}

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