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Print the last occurrence of elements in array in relative order
  • Difficulty Level : Medium
  • Last Updated : 20 Mar, 2019

Given an array of N elements, print the elements in the same relative order as given by removing all the occurrences of elements except the last occurrence.

Examples:

Input: a[] = {1, 5, 5, 1, 6, 1}
Output: 5 6 1
Remove two integers 1, which are in the positions 1 and 4. Also, remove the integer 5, which is in the position 2.
Hence the left array is {5, 6, 1}

Input: a[] = {2, 5, 5, 2}
Output: 5 2

Approach:



  • Hash the last occurrence of every element.
  • Iterate in the array of N elements, if the element’s index is hashed, then print the array element.

Below is the implementation of the above approach:

C++




// C++ program to print the last occurrence
// of every element in relative order
#include <bits/stdc++.h>
using namespace std;
  
// Function to print the last occurrence
// of every element in an array
void printLastOccurrence(int a[], int n)
{
  
    // used in hashing
    unordered_map<int, int> mp;
  
    // iterate and store the last index
    // of every element
    for (int i = 0; i < n; i++)
        mp[a[i]] = i;
  
    // iterate and check for the last
    // occurrence of every element
    for (int i = 0; i < n; i++) {
        if (mp[a[i]] == i)
            cout << a[i] << " ";
    }
}
// Driver Code
int main()
{
    int a[] = { 1, 5, 5, 1, 6, 1 };
    int n = sizeof(a) / sizeof(a[0]);
    printLastOccurrence(a, n);
  
    return 0;
}


Java




// Java program to print the 
// last occurrence of every 
// element in relative order
import java.util.*;
  
class GFG
{
      
    // Function to print the last 
    // occurrence of every element
    // in an array
    public static void printLastOccurrence(int a[],
                                           int n)
    {
        HashMap<Integer, 
                Integer> map = new HashMap<Integer, 
                                           Integer>();
          
        // iterate and store the last 
        // index of every element
        for (int i = 0; i < n; i++)
            map.put(a[i], i);
              
        for (int i = 0; i < n; i++)
        {
        if (map.get(a[i]) == i)
            System.out.print(a[i] +" ");
        
    }
      
    // Driver Code
    public static void main (String[] args)
    {
        int a[] = { 1, 5, 5, 1, 6, 1 };
        int n = a.length;
        printLastOccurrence(a, n);
    }
}
  
// This code is contributed
// by ankita_saini


Python3




# Python 3 program to print the last occurrence
# of every element in relative order
  
# Function to print the last occurrence
# of every element in an array
def printLastOccurrence(a, n):
      
    # used in hashing
    mp = {i:0 for i in range(7)}
  
    # iterate and store the last 
    # index of every element
    for i in range(n):
        mp[a[i]] = i
  
    # iterate and check for the last
    # occurrence of every element
    for i in range(n):
        if (mp[a[i]] == i):
            print(a[i], end = " ")
  
# Driver Code
if __name__ == '__main__':
    a = [1, 5, 5, 1, 6, 1]
    n = len(a)
    printLastOccurrence(a, n)
  
# This code is contributed by
# Surendra_Gangwar


C#




// C# program to print the 
// last occurrence of every 
// element in relative order
using System;
  
class GFG
{
      
// Function to print the last 
// occurrence of every element
// in an array
public static void printLastOccurrence(int[] a,
                                       int n)
{
    HashMap<Integer, 
            Integer> map = new HashMap<Integer, 
                                       Integer>();
      
    // iterate and store the last 
    // index of every element
    for (int i = 0; i < n; i++)
        map.put(a[i], i);
          
    for (int i = 0; i < n; i++)
    {
    if (map.get(a[i]) == i)
        Console.Write(a[i] + " ");
    
}
  
// Driver Code
public static void Main ()
{
    int[] a = { 1, 5, 5, 1, 6, 1 };
    int n = a.Length;
    printLastOccurrence(a, n);
}
}
  
// This code is contributed
// by ChitraNayal


PHP




<?php 
// PHP program to print the last 
// occurrence of every element 
// in relative order
  
// Function to print the last
// occurrence of every element
// in an array
function printLastOccurrence(&$a, $n)
{
  
    // used in hashing
    $mp = array();
  
    // iterate and store the last 
    // index of every element
    for ($i = 0; $i < $n; $i++)
        $mp[$a[$i]] = $i;
  
    // iterate and check for the last
    // occurrence of every element
    for ($i = 0; $i < $n; $i++) 
    {
        if ($mp[$a[$i]] == $i)
            echo $a[$i] . " ";
    }
}
  
// Driver Code
$a = array(1, 5, 5, 1, 6, 1);
$n = sizeof($a);
printLastOccurrence($a, $n);
  
// This code is contributed 
// by ChitraNayal
?>



Output:

5 6 1

Time Complexity: O(N * log N)

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