k-th missing element in an unsorted array
Given an unsorted sequence a[], the task is to find the K-th missing contiguous element in the increasing sequence of the array elements i.e. consider the array in sorted order and find the kth missing number. If no k-th missing element is there output -1.
Note: Only elements exists in the range of minimum and maximum element to be considered.
Examples:
Input: arr[] = {2, 4, 10, 7}, k = 5
Output: 9
Missing elements in the given array: 3, 5, 6, 8, 9
5th missing is 9.
Input: arr[] = {1, 3, 4}, k = 5
Output: -1
Method-1: Sort the array and use the approach used in the k-th missing element in a sorted array.
Method-2:
- Insert all the elements in an unordered_set.
- Find the minimum and maximum element of the array.
-
Traverse the elements from minimum to maximum.
- Check if current element is present in the set or not.
- If not then check if this is kth missing by counting the missing elements.
- Return the current element if this is current missing.
Below is the implementation of the above approach:
C++
// C++ implementation of the above approach #include <bits/stdc++.h> using namespace std; // Function to find the sum // of minimum of all subarrays int findKth(int arr[], int n, int k) { unordered_set<int> missing; int count = 0; // Insert all the elements in a set for (int i = 0; i < n; i++) missing.insert(arr[i]); // Find the maximum and minimum element int maxm = *max_element(arr, arr + n); int minm = *min_element(arr, arr + n); // Traverse from the minimum to maximum element for (int i = minm + 1; i < maxm; i++) { // Check if "i" is missing if (missing.find(i) == missing.end()) count++; // Check if it is kth missing if (count == k) return i; } // If no kth element is missing return -1; } // Driver code int main() { int arr[] = { 2, 10, 9, 4 }; int n = sizeof(arr) / sizeof(arr[0]); int k = 5; cout << findKth(arr, n, k); return 0; } |
Java
// Java implementation of the above approach import java.util.*; class GFG { // Function to find the sum // of minimum of all subarrays static int findKth(int arr[], int n, int k) { HashSet<Integer> missing = new HashSet<>(); int count = 0; // Insert all the elements in a set for (int i = 0; i < n; i++) { missing.add(arr[i]); } // Find the maximum and minimum element int maxm = Arrays.stream(arr).max().getAsInt(); int minm = Arrays.stream(arr).min().getAsInt(); // Traverse from the minimum to maximum element for (int i = minm+1; i < maxm; i++) { // Check if "i" is missing if (!missing.contains(i)) { count++; } // Check if it is kth missing if (count == k) { return i; } } // If no kth element is missing return -1; } // Driver code public static void main(String[] args) { int arr[] = {2, 10, 9, 4}; int n = arr.length; int k = 5; System.out.println(findKth(arr, n, k)); } } /* This code contributed by PrinciRaj1992 */ |
Python
# Python3 implementation of the above approach # Function to find the sum # of minimum of all subarrays def findKth( arr, n, k): missing = dict() count = 0 # Insert all the elements in a set for i in range(n): missing[arr[i]] = 1 # Find the maximum and minimum element maxm = max(arr) minm = min(arr) # Traverse from the minimum to maximum element for i in range(minm + 1, maxm): # Check if "i" is missing if (i not in missing.keys()): count += 1 # Check if it is kth missing if (count == k): return i # If no kth element is missing return -1 # Driver code arr = [2, 10, 9, 4 ] n = len(arr) k = 5print(findKth(arr, n, k)) # This code is contributed by Mohit Kumar |
C#
// C# implementation of the above approach using System; using System.Linq; using System.Collections.Generic; class GFG { // Function to find the sum // of minimum of all subarrays static int findKth(int []arr, int n, int k) { HashSet<int> missing = new HashSet<int>(); int count = 0; // Insert all the elements in a set for (int i = 0; i < n; i++) { missing.Add(arr[i]); } // Find the maximum and minimum element int maxm = arr.Max(); int minm = arr.Min(); // Traverse from the minimum to maximum element for (int i = minm + 1; i < maxm; i++) { // Check if "i" is missing if (!missing.Contains(i)) { count++; } // Check if it is kth missing if (count == k) { return i; } } // If no kth element is missing return -1; } // Driver code public static void Main(String[] args) { int []arr = {2, 10, 9, 4}; int n = arr.Length; int k = 5; Console.WriteLine(findKth(arr, n, k)); } } // This code has been contributed by 29AjayKumar |
PHP
<?php // PHP implementation of the above approach // Function to find the sum // of minimum of all subarrays function findKth($arr, $n, $k) { $missing = array(); $count = 0; // Insert all the elements in a set for ($i = 0; $i < $n; $i++) array_push($missing, $arr[$i]); $missing = array_unique($missing); // Find the maximum and minimum element $maxm = max($arr); $minm = min($arr); // Traverse from the minimum to // maximum element for ($i = $minm + 1; $i < $maxm; $i++) { // Check if "i" is missing if (!in_array($i, $missing, false)) $count += 1; // Check if it is kth missing if ($count == $k) return $i; } // If no kth element is missing return -1; } // Driver code $arr = array(2, 10, 9, 4); $n = sizeof($arr); $k = 5; echo findKth($arr, $n, $k); // This code is contributed by Ryuga ?> |
Output:
8
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