Tuesday, May 3, 2022

Question 11 : Find missing number in the array.

You are given an integer array containing 1 to n but one of the numbers from 1 to n in the array is missing. You need to provide the optimum solution to find the missing number. 

The number cannot be repeated in the array.:

int[] arr1={7,5,6,1,4,2}; Missing numner : 3 int[] arr2={5,3,1,2}; Missing numner : 4


  1. Find the sum of n number using formula n=n*(n+1)/2
  2. Find the sum of elements present in given array.
  3. Substract (sum of n numbers – sum of elements present in the array).

Java program to find missing number in an array:

public class MissingNumberMain { public static void main(String[] args) { int[] arr1={7,5,6,1,4,2}; System.out.println("Missing number from array arr1: "+missingNumber(arr1)); int[] arr2={5,3,1,2}; System.out.println("Missing number from array arr2: "+missingNumber(arr2)); } public static int missingNumber(int[] arr) { int n=arr.length+1; int sum=n*(n+1)/2; int restSum=0; for (int i = 0; i < arr.length; i++) { restSum+=arr[i]; } int missingNumber=sum-restSum; return missingNumber; } }

When you run the above program, you will get the below output:

Missing number from array arr1: 3 Missing number from array arr2: 4

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