Find elements which are present in first array and not in second

Given two arrays, the task is that we find numbers which are present in first array, but not present in the second array.
Examples :

Input : a[] = {1, 2, 3, 4, 5, 10};
b[] = {2, 3, 1, 0, 5};
Output : 4 10
4 and 10 are present in first array, but
not in second array.

Input : a[] = {4, 3, 5, 9, 11};
b[] = {4, 9, 3, 11, 10};
Output : 5

Method 1 (Simple)
A Naive Approach is to use two loops and check element which not present in second array.

C++

 // C++ simple program to  // find elements which are  // not present in second array #include using namespace std;    // Function for finding  // elements which are there  // in a[]  but not in b[]. void findMissing(int a[], int b[],                   int n, int m) {     for (int i = 0; i < n; i++)     {         int j;         for (j = 0; j < m; j++)             if (a[i] == b[j])                 break;            if (j == m)             cout << a[i] << " ";     } }    // Driver code int main() {     int a[] = { 1, 2, 6, 3, 4, 5 };     int b[] = { 2, 4, 3, 1, 0 };     int n = sizeof(a) / sizeof(a);     int m = sizeof(b) / sizeof(b);     findMissing(a, b, n, m);     return 0; }

Java

 // Java simple program to  // find elements which are  // not present in second array class GFG  {            // Function for finding elements      // which are there in a[] but not     // in b[].     static void findMissing(int a[], int b[],                              int n, int m)     {         for (int i = 0; i < n; i++)         {             int j;                            for (j = 0; j < m; j++)                 if (a[i] == b[j])                     break;                if (j == m)                 System.out.print(a[i] + " ");         }     }        // Driver Code     public static void main(String[] args)     {         int a[] = { 1, 2, 6, 3, 4, 5 };         int b[] = { 2, 4, 3, 1, 0 };                    int n = a.length;         int m = b.length;                    findMissing(a, b, n, m);     } }    // This code is contributed // by Anant Agarwal.

Python 3

 # Python 3 simple program to find elements  # which are not present in second array    # Function for finding elements which  # are there in a[] but not in b[]. def findMissing(a, b, n, m):        for i in range(n):         for j in range(m):             if (a[i] == b[j]):                 break            if (j == m - 1):             print(a[i], end = " ")    # Driver code if __name__ == "__main__":            a = [ 1, 2, 6, 3, 4, 5 ]     b = [ 2, 4, 3, 1, 0 ]     n = len(a)     m = len(b)     findMissing(a, b, n, m)    # This code is contributed  # by ChitraNayal

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C#

 // C# simple program to find elements // which are not present in second array using System;    class GFG {            // Function for finding elements      // which are there in a[] but not     // in b[].     static void findMissing(int []a, int []b,                              int n, int m)     {         for (int i = 0; i < n; i++)         {             int j;                            for (j = 0; j < m; j++)                 if (a[i] == b[j])                     break;                if (j == m)                 Console.Write(a[i] + " ");         }     }        // Driver code     public static void Main()     {         int []a = {1, 2, 6, 3, 4, 5};         int []b = {2, 4, 3, 1, 0};                    int n = a.Length;         int m = b.Length;                    findMissing(a, b, n, m);     } }    // This code is contributed by vt_m.

PHP



Output :

6 5

Method 2 (Use Hashing)
In this method, we store all elements of second array in a hash table (unordered_set). One by one check all elements of first array and print all those elements which are not present in the hash table.

C++

 // C++ efficient program to  // find elements which are not // present in second array #include using namespace std;    // Function for finding  // elements which are there  // in a[] but not in b[]. void findMissing(int a[], int b[],                   int n, int m) {     // Store all elements of      // second array in a hash table     unordered_set s;     for (int i = 0; i < m; i++)         s.insert(b[i]);        // Print all elements of      // first array that are not     // present in hash table     for (int i = 0; i < n; i++)         if (s.find(a[i]) == s.end())             cout << a[i] << " "; }    // Driver code int main() {     int a[] = { 1, 2, 6, 3, 4, 5 };     int b[] = { 2, 4, 3, 1, 0 };     int n = sizeof(a) / sizeof(a);     int m = sizeof(b) / sizeof(b);     findMissing(a, b, n, m);     return 0; }

Java

 // Java efficient program to find elements  // which are not present in second array  import java.util.HashSet; import java.util.Set;    public class GfG{        // Function for finding elements which       // are there in a[] but not in b[].      static void findMissing(int a[], int b[],                        int n, int m)      {          // Store all elements of           // second array in a hash table          HashSet s = new HashSet<>();          for (int i = 0; i < m; i++)              s.add(b[i]);                   // Print all elements of first array          // that are not present in hash table          for (int i = 0; i < n; i++)              if (!s.contains(a[i]))                 System.out.print(a[i] + " ");      }          public static void main(String []args){                    int a[] = { 1, 2, 6, 3, 4, 5 };          int b[] = { 2, 4, 3, 1, 0 };          int n = a.length;          int m = b.length;          findMissing(a, b, n, m);      } }      // This code is contributed by Rituraj Jain

Python3

 # Python3 efficient program to find elements  # which are not present in second array    # Function for finding elements which  # are there in a[] but not in b[]. def findMissing(a, b, n, m):            # Store all elements of second      # array in a hash table     s = dict()     for i in range(m):         s[b[i]] = 1        # Print all elements of first array      # that are not present in hash table     for i in range(n):         if a[i] not in s.keys():             print(a[i], end = " ")    # Driver code a = [ 1, 2, 6, 3, 4, 5 ] b = [ 2, 4, 3, 1, 0 ] n = len(a) m = len(b) findMissing(a, b, n, m)    # This code is contributed by mohit kumar

C#

 // C# efficient program to find elements  // which are not present in second array  using System;  using System.Collections.Generic;    class GfG {        // Function for finding elements which      // are there in a[] but not in b[].      static void findMissing(int []a, int []b,                      int n, int m)      {          // Store all elements of          // second array in a hash table          HashSet s = new HashSet();          for (int i = 0; i < m; i++)              s.Add(b[i]);                     // Print all elements of first array          // that are not present in hash table          for (int i = 0; i < n; i++)              if (!s.Contains(a[i]))                 Console.Write(a[i] + " ");      }         // Driver code     public static void Main(String []args)     {         int []a = { 1, 2, 6, 3, 4, 5 };          int []b = { 2, 4, 3, 1, 0 };          int n = a.Length;          int m = b.Length;          findMissing(a, b, n, m);     } }    /* This code contributed by PrinciRaj1992 */

Output :

6 5

Time complexity : O(n)
Auxiliary Space : O(n)