» » » Java Program to find missing numbers in an array

  • To find missing numbers in an array first we need to make sure that array is sorted.
  • After sorting we need to check that array each element with next element then we can find the difference.
  • if Array is not sorted :To sort array use Arrays.sort(array);
  • If difference is 1 then no need to do any thing because numbers are in order.
  • If difference is not equal to 1 then we need to print all those numbers or pick those numbers and place it in one array.
  • this would be the logic to find missing numbers in an array
  • Here there may be a chance of array not starts with 1 then we need to check first itself whether array starts with 1 or not if not we need to print 1 to starting element of array.
  • for example int a[]={4,5,6,8}; then we need to print 1 2 3  7.



 Lets see a java example program to find missing numbers in an array.

  1. package arraysInterviewQuestions;
  2. public class PrintMissingNumbers {
  3.  
  4. private static void findMissingNumber(int[] number){
  5.  
  6.         // take max length as last number in array
  7.     int k[] = new int[number[number.length-1]];
  8.         
  9.   int m=0;
  10.  
  11.   if(number[0]!=1){
  12.    for (int x = 1; x < number[0]; x++) {
  13.        k[m] =  x;
  14.        m++;
  15.        }
  16.   }
  17.         
  18.  for (int i = 0; i < number.length -1; i++) {
  19.     
  20.     int j = i+1;
  21.     int difference = number[j] - number[i] ;
  22.             
  23.             
  24.    if(difference != 1 ){
  25.         
  26.   for (int x = 1; x < difference; x++) {
  27.  
  28.           k[m] = number[i] + x;
  29.            m++;
  30.     
  31. }
  32.             
  33.  }
  34.  }
  35.         
  36. System.out.println("missing numbers in array ::");
  37.         
  38. for (int l = 0; l < m ; l++) {
  39.     System.out.println( k[l]+" ");
  40. }
  41. }
  42.  public static void main(String[] args) {
  43.         
  44.    int a[]= {2,4,6,9,10,20};
  45.  
  46.    //if Array is not sorted :To sort array use Arrays.sort(a); 
  47.  
  48.   findMissingNumber(a);
  49.  
  50.    
  51. }
  52. }
 
program to find missing number in an array in java


  • Change the array in main method and practice try to find missing elements in an array that contains 1 to 100 numbers.

Instance Of Java

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