# k-th missing element in sorted array

Given an increasing sequence a[], we need to find the K-th missing contiguous element in the increasing sequence which is not present in the sequence. If no k-th missing element is there output -1.

Examples :

Input : a[] = {2, 3, 5, 9, 10};
k = 1;
Output : 4
Explanation: Missing Element in the increasing
sequence are {4, 6, 7, 8}. So k-th missing element
is 4

Input : a[] = {2, 3, 5, 9, 10, 11, 12};
k = 4;
Output : 8
Explanation: missing element in the increasing
sequence are {4, 6, 7, 8}  so k-th missing
element is 8

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Start iterating over the array elements, and for every element check if next element is consecutive or not, if not, then take difference between these two, and check if difference is greater than or equal to given k, then calculate ans = a[i] + count, else iterate for next element.

 #include using namespace std;    // Function to find k-th  // missing element int missingK(int a[], int k,               int n) {     int difference = 0,          ans = 0, count = k;     bool flag = 0;            // interating over the array     for(int i = 0 ; i < n - 1; i++)     {            difference = 0;                    // check if i-th and          // (i + 1)-th element          // are not consecutive         if ((a[i] + 1) != a[i + 1])          {                            // save their difference             difference +=                  (a[i + 1] - a[i]) - 1;                            // check for difference             // and given k             if (difference >= count)                 {                     ans = a[i] + count;                     flag = 1;                     break;                 }             else                 count -= difference;         }     }            // if found     if(flag)         return ans;     else         return  -1; }    // Driver code int main() {     // Input array     int a[] = {1, 5, 11, 19};            // k-th missing element      // to be found in the array     int k = 11;     int n = sizeof(a) / sizeof(a[0]);            // calling function to     // find missing element     int missing = missingK(a, k, n);            cout << missing << endl;            return 0; }

 // Java program to check for // even or odd import java.io.*; import java.util.*;     public class GFG {             // Function to find k-th      // missing element     static int missingK(int []a, int k,                                   int n)     {         int difference = 0,              ans = 0, count = k;         boolean flag = false;                     // interating over the array         for(int i = 0 ; i < n - 1; i++)         {              difference = 0;                             // check if i-th and              // (i + 1)-th element              // are not consecutive             if ((a[i] + 1) != a[i + 1])              {                                     // save their difference                 difference +=                      (a[i + 1] - a[i]) - 1;                                     // check for difference                 // and given k                 if (difference >= count)                     {                         ans = a[i] + count;                         flag = true;                         break;                     }                 else                     count -= difference;             }         }                     // if found         if(flag)             return ans;         else             return -1;     }             // Driver code     public static void main(String args[])     {                     // Input array         int []a = {1, 5, 11, 19};                     // k-th missing element          // to be found in the array         int k = 11;         int n = a.length;                     // calling function to         // find missing element         int missing = missingK(a, k, n);                     System.out.print(missing);     }     }     // This code is contributed by // Manish Shaw (manishshaw1)

 # Function to find k-th  # missing element def missingK(a, k, n) :        difference = 0     ans = 0     count = k     flag = 0            # interating over the array     for i in range (0, n-1) :          difference = 0                    # check if i-th and          # (i + 1)-th element          # are not consecutive         if ((a[i] + 1) != a[i + 1]) :                                       # save their difference             difference += (a[i + 1] - a[i]) - 1                            # check for difference             # and given k             if (difference >= count) :                     ans = a[i] + count                     flag = 1                     break             else :                 count -= difference                 # if found     if(flag) :         return ans     else :         return -1    # Driver code # Input array a = [1, 5, 11, 19]    # k-th missing element  # to be found in the array k = 11 n = len(a)    # calling function to # find missing element missing = missingK(a, k, n)    print(missing)    # This code is contributed by  # Manish Shaw (manishshaw1)

 // C# program to check for // even or odd using System; using System.Collections.Generic;    class GFG {            // Function to find k-th      // missing element     static int missingK(int []a, int k,                                   int n)     {         int difference = 0,              ans = 0, count = k;         bool flag = false;                    // interating over the array         for(int i = 0 ; i < n - 1; i++)         {              difference = 0;                            // check if i-th and              // (i + 1)-th element              // are not consecutive             if ((a[i] + 1) != a[i + 1])              {                                    // save their difference                 difference +=                      (a[i + 1] - a[i]) - 1;                                    // check for difference                 // and given k                 if (difference >= count)                     {                         ans = a[i] + count;                         flag = true;                         break;                     }                 else                     count -= difference;             }         }                    // if found         if(flag)             return ans;         else             return -1;     }            // Driver code     public static void Main()     {                    // Input array         int []a = {1, 5, 11, 19};                    // k-th missing element          // to be found in the array         int k = 11;         int n = a.Length;                    // calling function to         // find missing element         int missing = missingK(a, k, n);                    Console.Write(missing);     }    }    // This code is contributed by // Manish Shaw (manishshaw1)

 = \$count)                 {                     \$ans = \$a[\$i] + \$count;                     \$flag = 1;                     break;                 }             else                 \$count -= \$difference;         }     }            // if found     if(\$flag)         return \$ans;     else         return -1; }    // Driver Code    // Input array \$a = array(1, 5, 11, 19);    // k-th missing element  // to be found in the array \$k = 11; \$n = count(\$a);    // calling function to // find missing element \$missing = missingK(\$a, \$k, \$n);    echo \$missing;    // This code is contributed by Manish Shaw // (manishshaw1) ?>

Output :
14

Time Complexity :O(n), where n is the number of elements in the array.

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