Elements that occurred only once in the array
Given an array arr that has numbers appearing twice or once. The task is to identify numbers that occur only once in the array.
Note: Duplicates appear side by side every time. There might be a few numbers that can occur at one time and just assume this is a right rotating array (just say an array can rotate k times towards right). The order of the elements in the output doesn’t matter.
Examples:
Input: arr[] = { 7, 7, 8, 8, 9, 1, 1, 4, 2, 2 } Output: 9 4 Input: arr[] = {-9, -8, 4, 4, 5, 5, -1} Output: -9 -8 -1
Method-1: Using Sorting.
- Sort the array.
- Check for each element at index i (except the first and last element), if
arr[i] != arr[i-1] && arr [i] != arr[i+1]
- For the first element, check if arr[0] != arr[1].
- For the last element, check if arr[n-1] != arr[n-2].
Algorithm:
- Sort the given array in non-decreasing order using any sorting algorithm.
- Traverse the sorted array and compare each element with its adjacent element.
- If an element is not equal to its adjacent elements, then print it.
- For the first element, check if it is different from the second element. If yes, print it.
- For the last element, check if it is different from the second last element. If yes, print it.
Pseudocode:
occurredOnce(arr[], n): sort(arr, arr + n) for i = 0 to n-1 do if i == 0 and arr[i] != arr[i+1] then print arr[i] else if i == n-1 and arr[i] != arr[i-1] then print arr[i] else if arr[i] != arr[i-1] and arr[i] != arr[i+1] then print arr[i]
Below is the implementation of the above approach:
C++
// C++ implementation of above approach #include <bits/stdc++.h> using namespace std; // Function to find the elements that // appeared only once in the array void occurredOnce( int arr[], int n) { // Sort the array sort(arr, arr + n); // Check for first element if (arr[0] != arr[1]) cout << arr[0] << " " ; // Check for all the elements if it is different // its adjacent elements for ( int i = 1; i < n - 1; i++) if (arr[i] != arr[i + 1] && arr[i] != arr[i - 1]) cout << arr[i] << " " ; // Check for the last element if (arr[n - 2] != arr[n - 1]) cout << arr[n - 1] << " " ; } // Driver code int main() { int arr[] = { 7, 7, 8, 8, 9, 1, 1, 4, 2, 2 }; int n = sizeof (arr) / sizeof (arr[0]); occurredOnce(arr, n); return 0; } |
Java
// Java implementation // of above approach import java.util.*; class GFG { // Function to find the elements that // appeared only once in the array static void occurredOnce( int arr[], int n) { // Sort the array Arrays.sort(arr); // Check for first element if (arr[ 0 ] != arr[ 1 ]) System.out.println(arr[ 0 ] + " " ); // Check for all the elements // if it is different // its adjacent elements for ( int i = 1 ; i < n - 1 ; i++) if (arr[i] != arr[i + 1 ] && arr[i] != arr[i - 1 ]) System.out.print(arr[i] + " " ); // Check for the last element if (arr[n - 2 ] != arr[n - 1 ]) System.out.print(arr[n - 1 ] + " " ); } // Driver code public static void main(String args[]) { int arr[] = { 7 , 7 , 8 , 8 , 9 , 1 , 1 , 4 , 2 , 2 }; int n = arr.length; occurredOnce(arr, n); } } // This code is contributed // by Arnab Kundu |
Python3
# Python 3 implementation # of above approach # Function to find the elements # that appeared only once in # the array def occurredOnce(arr, n): # Sort the array arr.sort() # Check for first element if arr[ 0 ] ! = arr[ 1 ]: print (arr[ 0 ], end = " " ) # Check for all the elements # if it is different its # adjacent elements for i in range ( 1 , n - 1 ): if (arr[i] ! = arr[i + 1 ] and arr[i] ! = arr[i - 1 ]): print ( arr[i], end = " " ) # Check for the last element if arr[n - 2 ] ! = arr[n - 1 ]: print (arr[n - 1 ], end = " " ) # Driver code if __name__ = = "__main__" : arr = [ 7 , 7 , 8 , 8 , 9 , 1 , 1 , 4 , 2 , 2 ] n = len (arr) occurredOnce(arr, n) # This code is contributed # by ChitraNayal |
Javascript
<script> // Javascript implementation // of above approach // Function to find the elements that // appeared only once in the array function occurredOnce(arr,n) { // Sort the array arr.sort( function (a,b){ return a-b;}); // Check for first element if (arr[0] != arr[1]) document.write(arr[0] + " " ); // Check for all the elements // if it is different // its adjacent elements for (let i = 1; i < n - 1; i++) if (arr[i] != arr[i + 1] && arr[i] != arr[i - 1]) document.write(arr[i] + " " ); // Check for the last element if (arr[n - 2] != arr[n - 1]) document.write(arr[n - 1] + " " ); } // Driver code let arr=[7, 7, 8, 8, 9, 1, 1, 4, 2, 2]; let n = arr.length; occurredOnce(arr, n); // This code is contributed by rag2127 </script> |
C#
// C# implementation // of above approach using System; class GFG { // Function to find the elements that // appeared only once in the array static void occurredOnce( int [] arr, int n) { // Sort the array Array.Sort(arr); // Check for first element if (arr[0] != arr[1]) Console.Write(arr[0] + " " ); // Check for all the elements // if it is different // its adjacent elements for ( int i = 1; i < n - 1; i++) if (arr[i] != arr[i + 1] && arr[i] != arr[i - 1]) Console.Write(arr[i] + " " ); // Check for the last element if (arr[n - 2] != arr[n - 1]) Console.Write(arr[n - 1] + " " ); } // Driver code public static void Main() { int [] arr = {7, 7, 8, 8, 9, 1, 1, 4, 2, 2}; int n = arr.Length; occurredOnce(arr, n); } } // This code is contributed // by ChitraNayal |
PHP
<?php // PHP implementation // of above approach // Function to find the elements // that appeared only once in // the array function occurredOnce(& $arr , $n ) { // Sort the array sort( $arr ); // Check for first element if ( $arr [0] != $arr [1]) echo $arr [0]. " " ; // Check for all the elements // if it is different its // adjacent elements for ( $i = 1; $i < $n - 1; $i ++) if ( $arr [ $i ] != $arr [ $i + 1] && $arr [ $i ] != $arr [ $i - 1]) echo $arr [ $i ]. " " ; // Check for the last element if ( $arr [ $n - 2] != $arr [ $n - 1]) echo $arr [ $n - 1]. " " ; } // Driver code $arr = array (7, 7, 8, 8, 9, 1, 1, 4, 2, 2); $n = sizeof( $arr ); occurredOnce( $arr , $n ); // This code is contributed // by ChitraNayal ?> |
4 9
Complexity Analysis:
- Time Complexity: O(Nlogn)
- Auxiliary Space: O(1)
Method-2: (Using Hashing): In C++, unordered_map can be used for hashing.
- Traverse the array.
- Store each element with its occurrence in the unordered_map.
- Traverse the unordered_map and print all the elements with occurrence 1.
Below is the implementation of the above approach:
C++
// C++ implementation to find elements // that appeared only once #include <bits/stdc++.h> using namespace std; // Function to find the elements that // appeared only once in the array void occurredOnce( int arr[], int n) { unordered_map< int , int > mp; // Store all the elements in the map with // their occurrence for ( int i = 0; i < n; i++) mp[arr[i]]++; // Traverse the map and print all the // elements with occurrence 1 for ( auto it = mp.begin(); it != mp.end(); it++) if (it->second == 1) cout << it->first << " " ; } // Driver code int main() { int arr[] = { 7, 7, 8, 8, 9, 1, 1, 4, 2, 2 }; int n = sizeof (arr) / sizeof (arr[0]); occurredOnce(arr, n); return 0; } |
Java
// Java implementation to find elements // that appeared only once import java.util.*; import java.io.*; class GFG { // Function to find the elements that // appeared only once in the array static void occurredOnce( int [] arr, int n) { HashMap<Integer, Integer> mp = new HashMap<>(); // Store all the elements in the map with // their occurrence for ( int i = 0 ; i < n; i++) { if (mp.containsKey(arr[i])) mp.put(arr[i], 1 + mp.get(arr[i])); else mp.put(arr[i], 1 ); } // Traverse the map and print all the // elements with occurrence 1 for (Map.Entry entry : mp.entrySet()) { if (Integer.parseInt(String.valueOf(entry.getValue())) == 1 ) System.out.print(entry.getKey() + " " ); } } // Driver code public static void main(String args[]) { int [] arr = { 7 , 7 , 8 , 8 , 9 , 1 , 1 , 4 , 2 , 2 }; int n = arr.length; occurredOnce(arr, n); } } // This code is contributed by rachana soma |
Python3
# Python3 implementation to find elements # that appeared only once import math as mt # Function to find the elements that # appeared only once in the array def occurredOnce(arr, n): mp = dict () # Store all the elements in the # map with their occurrence for i in range (n): if arr[i] in mp.keys(): mp[arr[i]] + = 1 else : mp[arr[i]] = 1 # Traverse the map and print all # the elements with occurrence 1 for it in mp: if mp[it] = = 1 : print (it, end = " " ) # Driver code arr = [ 7 , 7 , 8 , 8 , 9 , 1 , 1 , 4 , 2 , 2 ] n = len (arr) occurredOnce(arr, n) # This code is contributed by # Mohit Kumar 29 |
Javascript
<script> // Javascript implementation to find elements // that appeared only once // Function to find the elements that // appeared only once in the array function occurredOnce(arr, n) { let mp = new Map(); // Store all the elements in the map // with their occurrence for (let i = 0; i < n; i++) { if (mp.has(arr[i])) mp.set(arr[i], 1 + mp.get(arr[i])); else mp.set(arr[i], 1); } // Traverse the map and print all the // elements with occurrence 1 for (let [key, value] of mp.entries()) { if (value == 1) document.write(key + " " ); } } // Driver code let arr = [ 7, 7, 8, 8, 9, 1, 1, 4, 2, 2 ]; let n = arr.length; occurredOnce(arr, n); // This code is contributed by avanitrachhadiya2155 </script> |
C#
// C# implementation to find elements // that appeared only once using System; using System.Collections.Generic; class GFG { // Function to find the elements that // appeared only once in the array static void occurredOnce( int [] arr, int n) { Dictionary< int , int > mp = new Dictionary< int , int >(); // Store all the elements in the map with // their occurrence for ( int i = 0; i < n; i++) { if (mp.ContainsKey(arr[i])) mp[arr[i]] = 1 + mp[arr[i]]; else mp.Add(arr[i], 1); } // Traverse the map and print all the // elements with occurrence 1 foreach (KeyValuePair< int , int > entry in mp) { if (Int32.Parse(String.Join( "" , entry.Value)) == 1) Console.Write(entry.Key + " " ); } } // Driver code public static void Main(String []args) { int [] arr = { 7, 7, 8, 8, 9, 1, 1, 4, 2, 2 }; int n = arr.Length; occurredOnce(arr, n); } } // This code is contributed by shikhasingrajput |
4 9
Complexity Analysis:
- Time Complexity: O(N)
- Auxiliary Space: O(N)
Method-3: Using given assumptions.
It is given that an array can be rotated any time and duplicates will appear side by side every time. So, after rotating, the first and last elements will appear side by side.
- Check if the first and last elements are equal. If yes, then start traversing the elements between them.
- Check if the current element is equal to the element in the immediate previous index. If yes, check the same for the next element.
- If not, print the current element.
Implementation:
C++
// C++ implementation to find elements // that appeared only once #include <bits/stdc++.h> using namespace std; // Function to find the elements that // appeared only once in the array void occurredOnce( int arr[], int n) { int i = 1, len = n; // Check if the first and last element is equal // If yes, remove those elements if (arr[0] == arr[len - 1]) { i = 2; len--; } // Start traversing the remaining elements for (; i < n; i++) // Check if current element is equal to // the element at immediate previous index // If yes, check the same for next element if (arr[i] == arr[i - 1]) i++; // Else print the current element else cout << arr[i - 1] << " " ; // Check for the last element if (arr[n - 1] != arr[0] && arr[n - 1] != arr[n - 2]) cout << arr[n - 1]; } // Driver code int main() { int arr[] = { 7, 7, 8, 8, 9, 1, 1, 4, 2, 2 }; int n = sizeof (arr) / sizeof (arr[0]); occurredOnce(arr, n); return 0; } |
Java
// Java implementation to find // elements that appeared only once class GFG { // Function to find the elements that // appeared only once in the array static void occurredOnce( int arr[], int n) { int i = 1 , len = n; // Check if the first and last // element is equal. If yes, // remove those elements if (arr[ 0 ] == arr[len - 1 ]) { i = 2 ; len--; } // Start traversing the // remaining elements for (; i < n; i++) // Check if current element is // equal to the element at // immediate previous index // If yes, check the same // for next element if (arr[i] == arr[i - 1 ]) i++; // Else print the current element else System.out.print(arr[i - 1 ] + " " ); // Check for the last element if (arr[n - 1 ] != arr[ 0 ] && arr[n - 1 ] != arr[n - 2 ]) System.out.print(arr[n - 1 ]); } // Driver code public static void main(String args[]) { int arr[] = { 7 , 7 , 8 , 8 , 9 , 1 , 1 , 4 , 2 , 2 }; int n = arr.length; occurredOnce(arr, n); } } // This code is contributed // by Arnab Kundu |
Python3
# Python 3 implementation to find # elements that appeared only once # Function to find the elements that # appeared only once in the array def occurredOnce(arr, n): i = 1 len = n # Check if the first and # last element is equal # If yes, remove those elements if arr[ 0 ] = = arr[ len - 1 ]: i = 2 len - = 1 # Start traversing the # remaining elements while i < n: # Check if current element is # equal to the element at # immediate previous index # If yes, check the same for # next element if arr[i] = = arr[i - 1 ]: i + = 1 # Else print the current element else : print (arr[i - 1 ], end = " " ) i + = 1 # Check for the last element if (arr[n - 1 ] ! = arr[ 0 ] and arr[n - 1 ] ! = arr[n - 2 ]): print (arr[n - 1 ]) # Driver code if __name__ = = "__main__" : arr = [ 7 , 7 , 8 , 8 , 9 , 1 , 1 , 4 , 2 , 2 ] n = len (arr) occurredOnce(arr, n) # This code is contributed # by ChitraNayal |
Javascript
<script> // Javascript implementation to find // elements that appeared only once // Function to find the elements that // appeared only once in the array function occurredOnce(arr, n) { var i = 1, len = n; // Check if the first and last // element is equal. If yes, // remove those elements if (arr[0] == arr[len - 1]) { i = 2; len--; } // Start traversing the // remaining elements for (; i < n; i++) // Check if current element is // equal to the element at // immediate previous index // If yes, check the same // for next element if (arr[i] == arr[i - 1]) i++; // Else print the current element else document.write(arr[i - 1] + " " ); // Check for the last element if (arr[n - 1] != arr[0] && arr[n - 1] != arr[n - 2]) document.write(arr[n - 1]); } // Driver code var arr = [ 7, 7, 8, 8, 9, 1, 1, 4, 2, 2 ]; var n = arr.length; occurredOnce(arr, n); // This code is contributed by Ankita saini </script> |
C#
// C# implementation to find // elements that appeared only once using System; class GFG { // Function to find the elements that // appeared only once in the array static void occurredOnce( int [] arr, int n) { int i = 1, len = n; // Check if the first and last // element is equal. If yes, // remove those elements if (arr[0] == arr[len - 1]) { i = 2; len--; } // Start traversing the // remaining elements for (; i < n; i++) // Check if current element is // equal to the element at // immediate previous index // If yes, check the same // for next element if (arr[i] == arr[i - 1]) i++; // Else print the current element else Console.Write(arr[i - 1] + " " ); // Check for the last element if (arr[n - 1] != arr[0] && arr[n - 1] != arr[n - 2]) Console.Write(arr[n - 1]); } // Driver code public static void Main() { int [] arr = {7, 7, 8, 8, 9, 1, 1, 4, 2, 2}; int n = arr.Length; occurredOnce(arr, n); } } // This code is contributed // by ChitraNayal |
PHP
<?php // PHP implementation to find // elements that appeared only once // Function to find the elements that // appeared only once in the array function occurredOnce(& $arr , $n ) { $i = 1; $len = $n ; // Check if the first and last // element is equal. If yes, // remove those elements if ( $arr [0] == $arr [ $len - 1]) { $i = 2; $len --; } // Start traversing the // remaining elements for (; $i < $n ; $i ++) // Check if current element is // equal to the element at // immediate previous index // If yes, check the same for // next element if ( $arr [ $i ] == $arr [ $i - 1]) $i ++; // Else print the current element else echo $arr [ $i - 1] . " " ; // Check for the last element if ( $arr [ $n - 1] != $arr [0] && $arr [ $n - 1] != $arr [ $n - 2]) echo $arr [ $n - 1]; } // Driver code $arr = array (7, 7, 8, 8, 9, 1, 1, 4, 2, 2); $n = sizeof( $arr ); occurredOnce( $arr , $n ); // This code is contributed // by ChitraNayal ?> |
9 4
Complexity Analysis:
- Time Complexity: O(N)
- Auxiliary Space: O(1)
Method #4:Using built-in Python functions:
- Count the frequencies of every element using the Counter function
- Traverse the frequency array and print all the elements with occurrence 1.
Below is the implementation
C++
// C++ program for the above approach #include<bits/stdc++.h> using namespace std; // Function to find the elements that // appeared only once in the array void OccurredOnce( int arr[], int n) { // counting frequency of every element // using unordered_map unordered_map< int , int > mp; for ( int i=0;i<n;i++){ mp[arr[i]]++; } // Traverse the map and print all // the elements with occurrence 1 for ( auto item: mp){ if (item.second == 1) { cout<<item.first<< " " ; } } } // Driver code int main() { int arr[] = {-9, -8, 4, 4, 5, 5, -1}; int n = sizeof (arr)/ sizeof (arr[0]); OccurredOnce(arr, n); return 0; } // This code is contributed by adityashatmfh |
Java
import java.util.HashMap; public class Main { public static void OccurredOnce( int [] arr) { // Counting frequency of every element using HashMap HashMap<Integer, Integer> mp = new HashMap<>(); for ( int i = 0 ; i < arr.length; i++) { if (mp.containsKey(arr[i])) { mp.put(arr[i], mp.get(arr[i]) + 1 ); } else { mp.put(arr[i], 1 ); } } // Traverse the map and print all the elements with occurrence 1 for ( int it : mp.keySet()) { if (mp.get(it) == 1 ) { System.out.print(it + " " ); } } } public static void main(String[] args) { int [] arr = { 7 , 7 , 8 , 8 , 9 , 1 , 1 , 4 , 2 , 2 }; OccurredOnce(arr); } } |
Python3
# Python3 implementation to find elements # that appeared only once from collections import Counter # Function to find the elements that # appeared only once in the array def occurredOnce(arr, n): #counting frequency of every element using Counter mp = Counter(arr) # Traverse the map and print all # the elements with occurrence 1 for it in mp: if mp[it] = = 1 : print (it, end = " " ) # Driver code arr = [ 7 , 7 , 8 , 8 , 9 , 1 , 1 , 4 , 2 , 2 ] n = len (arr) occurredOnce(arr, n) # This code is contributed by vikkycirus |
Javascript
function occurredOnce(arr, n) { // counting frequency of every element // using Map let mp = new Map(); for (let i=0; i<n; i++) { mp.set(arr[i], (mp.get(arr[i]) || 0) + 1); } // Traverse the map and print all // the elements with occurrence 1 for (let [key, value] of mp) { if (value == 1) { console.log(key + " " ); } } } // Driver code let arr = [-9, -8, 4, 4, 5, 5, -1]; let n = arr.length; occurredOnce(arr, n); |
C#
// C# program for the above approach using System; using System.Collections.Generic; using System.Linq; class Program { // Function to find the elements that // appeared only once in the array static void OccurredOnce( int [] arr, int n) { // counting frequency of every element using .Count() method Dictionary< int , int > mp = arr.GroupBy(x => x).ToDictionary(g => g.Key, g => g.Count()); // Traverse the map and print all // the elements with occurrence 1 foreach ( var item in mp) { if (item.Value == 1) { Console.Write(item.Key + " " ); } } } // Driver code static void Main( string [] args) { int [] arr = {7, 7, 8, 8, 9, 1, 1, 4, 2, 2}; int n = arr.Length; OccurredOnce(arr, n); } } // This code is contributed by Prince Kumar |
9 4
Time Complexity: O(n)
Auxiliary Space: O(n)