# 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
```

## Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

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 `

## 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 <``int``> 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<``int``> s = ``new` `HashSet<``int``>();  ` `        ``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)

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