Find missing number in another array which is shuffled copy

Last Updated : 11 Jul, 2022

Given an array 'arr1' of n positive integers. Contents of arr1[] are copied to another array 'arr2', but numbers are shuffled and one element is removed. Find the missing element(without using any extra space and in O(n) time complexity).

Examples :

Input : arr1[] = {4, 8, 1, 3, 7},          arr2[] = {7, 4, 3, 1} Output : 8  Input : arr1[] = {12, 10, 15, 23, 11, 30},          arr2[] = {15, 12, 23, 11, 30} Output : 10

A simple solution is to one by one consider every element of first array and search in second array. As soon as we find a missing element, we return. Time complexity of this solution is O(n²)

An efficient solution is based on XOR. The combined occurrence of each element is twice, one in 'arr1' and other in 'arr2', except one element which only has a single occurrence in 'arr1'. We know that (a Xor a) = 0. So, simply XOR the elements of both the arrays. The result will be the missing number.

Implementation:

C++

// C++ implementation to find the // missing number in shuffled array // C++ implementation to find the // missing number in shuffled array #include <bits/stdc++.h> using namespace std;  // Returns the missing number // Size of arr2[] is n-1 int missingNumber(int arr1[], int arr2[],                                     int n) {     // Missing number 'mnum'     int mnum = 0;      // 1st array is of size 'n'     for (int i = 0; i < n; i++)         mnum = mnum ^ arr1[i];      // 2nd array is of size 'n - 1'     for (int i = 0; i < n - 1; i++)         mnum = mnum ^ arr2[i];      // Required missing number     return mnum; }  // Driver Code int main() {     int arr1[] = {4, 8, 1, 3, 7};     int arr2[] = {7, 4, 3, 1};     int n = sizeof(arr1) / sizeof(arr1[0]);     cout << "Missing number = "         << missingNumber(arr1, arr2, n);     return 0; }

Java

// Java implementation to find the // missing number in shuffled array  class GFG  {     // Returns the missing number     // Size of arr2[] is n-1     static int missingNumber(int arr1[],                               int arr2[],                                   int n)     {         // Missing number 'mnum'         int mnum = 0;              // 1st array is of size 'n'         for (int i = 0; i < n; i++)             mnum = mnum ^ arr1[i];              // 2nd array is of size 'n - 1'         for (int i = 0; i < n - 1; i++)             mnum = mnum ^ arr2[i];              // Required missing number         return mnum;     }          // Driver Code     public static void main (String[] args)      {         int arr1[] = {4, 8, 1, 3, 7};         int arr2[] = {7, 4, 3, 1};         int n = arr1.length;                  System.out.println("Missing number = "             + missingNumber(arr1, arr2, n));     } }

Python3

# Python3 implementation to find the # missing number in shuffled array  # Returns the missing number # Size of arr2[] is n - 1 def missingNumber(arr1, arr2, n):      # missing number 'mnum'     mnum = 0      # 1st array is of size 'n'     for i in range(n):         mnum = mnum ^ arr1[i]      # 2nd array is of size 'n - 1'     for i in range(n - 1):         mnum = mnum ^ arr2[i]      # Required missing number     return mnum  # Driver Code arr1 = [4, 8, 1, 3, 7] arr2= [7, 4, 3, 1] n = len(arr1) print("Missing number = ",      missingNumber(arr1, arr2, n))          # This code is contributed by Anant Agarwal.

 // C# implementation to find the // missing number in shuffled array using System;  class GFG {     // Returns the missing number     // Size of arr2[] is n-1     static int missingNumber(int []arr1,                               int []arr2,                                    int n)     {         // Missing number 'mnum'         int mnum = 0;              // 1st array is of size 'n'         for (int i = 0; i < n; i++)             mnum = mnum ^ arr1[i];              // 2nd array is of size 'n - 1'         for (int i = 0; i < n - 1; i++)             mnum = mnum ^ arr2[i];              // Required missing number         return mnum;     }          // Driver Code     public static void Main ()      {         int []arr1 = {4, 8, 1, 3, 7};         int []arr2 = {7, 4, 3, 1};         int n = arr1.Length;              Console.Write("Missing number = "             + missingNumber(arr1, arr2, n));     } }  // This code is contributed by nitin mittal.

PHP

<?php // PHP implementation to find the // missing number in shuffled array // PHP implementation to find the // missing number in shuffled array  // Returns the missing number // Size of arr2[] is n-1 function missingNumber($arr1, $arr2,                                  $n) {          // Missing number 'mnum'     $mnum = 0;      // 1st array is of size 'n'     for ($i = 0; $i < $n; $i++)         $mnum = $mnum ^ $arr1[$i];      // 2nd array is of size 'n - 1'     for ($i = 0; $i < $n - 1; $i++)         $mnum = $mnum ^ $arr2[$i];      // Required missing number     return $mnum; }      // Driver Code     $arr1 = array(4, 8, 1, 3, 7);     $arr2 = array(7, 4, 3, 1);     $n = count($arr1);     echo "Missing number = "         , missingNumber($arr1, $arr2, $n);          // This code is contributed by anuj_67.  ?>

JavaScript

<script>  // Javascript implementation to find the // missing number in shuffled array // Javascript implementation to find the // missing number in shuffled array  // Returns the missing number // Size of arr2[] is n-1 function missingNumber(arr1, arr2, n) {     // Missing number 'mnum'     let mnum = 0;      // 1st array is of size 'n'     for (let i = 0; i < n; i++)         mnum = mnum ^ arr1[i];      // 2nd array is of size 'n - 1'     for (let i = 0; i < n - 1; i++)         mnum = mnum ^ arr2[i];      // Required missing number     return mnum; }  // Driver Code     let arr1 = [4, 8, 1, 3, 7];     let arr2 = [7, 4, 3, 1];     let n = arr1.length;     document.write("Missing number = "         + missingNumber(arr1, arr2, n));  </script>

Output

Missing number = 8

Time Complexity: O(n).
Space Complexity: O(1).

Find whether an array is subset of another array using Map

Ayush Jauhari

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Find missing number in another array which is shuffled copy

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