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<bits/stdc++.h>` `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[0]);` ` ` `int` `m = ` `sizeof` `(b) / ` `sizeof` `(b[1]);` ` ` `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

`<?php` `// PHP 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[].` `function` `findMissing( ` `$a` `, ` `$b` `, ` `$n` `, ` `$m` `)` `{` ` ` `for` `( ` `$i` `= 0; ` `$i` `< ` `$n` `; ` `$i` `++)` ` ` `{` ` ` `$j` `;` ` ` `for` `(` `$j` `= 0; ` `$j` `< ` `$m` `; ` `$j` `++)` ` ` `if` `(` `$a` `[` `$i` `] == ` `$b` `[` `$j` `])` ` ` `break` `;` ` ` `if` `(` `$j` `== ` `$m` `)` ` ` `echo` `$a` `[` `$i` `] , ` `" "` `;` ` ` `}` `}` `// Driver code` `$a` `= ` `array` `( 1, 2, 6, 3, 4, 5 );` `$b` `= ` `array` `( 2, 4, 3, 1, 0 );` `$n` `= ` `count` `(` `$a` `);` `$m` `= ` `count` `(` `$b` `);` `findMissing(` `$a` `, ` `$b` `, ` `$n` `, ` `$m` `);` `// This code is contributed by anuj_67.` `?>` |

## Javascript

`<script>` `// Javascript 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[].` ` ` `function` `findMissing(a,b,n,m)` ` ` `{` ` ` `for` `(let i = 0; i < n; i++)` ` ` `{` ` ` `let j;` ` ` ` ` `for` `(j = 0; j < m; j++)` ` ` `if` `(a[i] == b[j])` ` ` `break` `;` ` ` ` ` `if` `(j == m)` ` ` `document.write(a[i] + ` `" "` `);` ` ` `}` ` ` `}` ` ` ` ` `// Driver Code` ` ` `let a=[ 1, 2, 6, 3, 4, 5 ];` ` ` `let b=[2, 4, 3, 1, 0];` ` ` `let n = a.length;` ` ` `let m = b.length;` ` ` `findMissing(a, b, n, m);` ` ` ` ` ` ` `// This code is contributed by avanitrachhadiya2155` ` ` `</script>` |

**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<bits/stdc++.h>` `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[0]);` ` ` `int` `m = ` `sizeof` `(b) / ` `sizeof` `(b[1]);` ` ` `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<Integer> 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 */` |

## Javascript

`<script>` `// Javascript 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[].` ` ` `function` `findMissing(a,b,n,m)` ` ` `{` ` ` `// Store all elements of` ` ` `// second array in a hash table` ` ` `let s = ` `new` `Set();` ` ` `for` `(let i = 0; i < m; i++)` ` ` `s.add(b[i]);` ` ` ` ` `// Print all elements of first array` ` ` `// that are not present in hash table` ` ` `for` `(let i = 0; i < n; i++)` ` ` `if` `(!s.has(a[i]))` ` ` `document.write(a[i] + ` `" "` `);` ` ` `}` ` ` ` ` `let a=[1, 2, 6, 3, 4, 5 ];` ` ` `let b=[2, 4, 3, 1, 0];` ` ` `let n = a.length;` ` ` `let m = b.length;` ` ` `findMissing(a, b, n, m);` ` ` `// This code is contributed by patel2127` `</script>` |

**Output :**

6 5

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

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