Find the smallest positive number missing from an unsorted array | Set 3

Given an unsorted array with both positive and negative elements. The task is to find the smallest positive number missing from the array.

Examples:

Input: arr[] = {2, 3, 7, 6, 8, -1, -10, 15}
Output: 1

Input: arr[] = { 2, 3, -7, 6, 8, 1, -10, 15 }
Output: 4

Input: arr[] = {1, 1, 0, -1, -2}
Output: 2



Approach :
We have already discussed some of the techniques to find the smallest positive number missing from an unsorted array.

Find the smallest positive number missing from an unsorted array | Set 1
Find the smallest positive number missing from an unsorted array | Set 2

Here, we use set to store all positive integers and find the first missing positive integer.

C++

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// CPP program to find the smallest
// positive missing number
#include <bits/stdc++.h>
using namespace std;
  
// Function to find the smallest
// positive missing number
int findMissingPositive(int arr[], int n)
{
    // Default smallest Positive Integer
    int m = 1;
  
    // Store values in set which are
    // greater than variable m
    set<int> x;
  
    for (int i = 0; i < n; i++) {
        // Store value when m is less than
        // current index of given array
        if (m < arr[i]) {
            x.insert(arr[i]);
        }
        else if (m == arr[i]) {
            // Increment m when it is equal
            // to current element
            m = m + 1;
  
            while (x.count(m)) {
                x.erase(m);
  
                // Increment m when it is one of the
                // element of the set
                m = m + 1;
            }
        }
    }
  
    // Return the required answer
    return m;
}
  
// Driver code
int main()
{
    int arr[] = { 2, 3, -7, 6, 8, 1, -10, 15 };
  
    int n = sizeof(arr) / sizeof(arr[0]);
  
    // Function call
    cout << findMissingPositive(arr, n);
  
    return 0;
}

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Java














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// Java program to find the smallest 


// positive missing number 


import java.util.*; 


  


class GFG 


{ 


  


// Function to find the smallest 


// positive missing number 


static int findMissingPositive(int arr[], int n) 


{ 


    // Default smallest Positive Integer 


    int m = 1; 


  


    // Store values in set which are 


    // greater than variable m 


    HashSet<Integer> x = new HashSet<Integer>(); 


  


    for (int i = 0; i < n; i++) 


    { 


        // Store value when m is less than 


        // current index of given array 


        if (m < arr[i]) 


        { 


            x.add(arr[i]); 


        } 


        else if (m == arr[i]) 


        { 


            // Increment m when it is equal 


            // to current element 


            m = m + 1; 


  


            while (x.contains(m))  


            { 


                x.remove(m); 


  


                // Increment m when it is one of the 


                // element of the set 


                m = m + 1; 


            } 


        } 


    } 


  


    // Return the required answer 


    return m; 


} 


  


// Driver code 


public static void main(String[] args)  


{ 


    int arr[] = { 2, 3, -7, 6, 8, 1, -10, 15 }; 


  


    int n = arr.length; 


  


    // Function call 


    System.out.println(findMissingPositive(arr, n)); 


} 


} 


  


// This code is contributed by 29AjayKumar 



















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Python3














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# Python 3 program to find the smallest 


# positive missing number 


  


# Function to find the smallest 


# positive missing number 


def findMissingPositive(arr, n): 


      


    # Default smallest Positive Integer 


    m = 1


  


    # Store values in set which are 


    # greater than variable m 


    x = [] 


    for i in range(n): 


          


        # Store value when m is less than 


        # current index of given array 


        if (m < arr[i]): 


            x.append(arr[i]) 


      


        elif (m == arr[i]): 


              


            # Increment m when it is equal 


            # to current element 


            m = m + 1


  


            while (x.count(m)): 


                x.remove(m) 


  


                # Increment m when it is one of the 


                # element of the set 


                m = m + 1


  


    # Return the required answer 


    return m 


  


# Driver code 


if __name__ == '__main__': 


    arr = [2, 3, -7, 6, 8, 1, -10, 15] 


  


    n = len(arr) 


  


    # Function call 


    print(findMissingPositive(arr, n)) 


  


# This code is contributed by 


# Surendra_Gangwar 



















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C#














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// C# program to find the smallest 


// positive missing number 


using System; 


using System.Collections.Generic; 


      


class GFG 


{ 


  


// Function to find the smallest 


// positive missing number 


static int findMissingPositive(int []arr, int n) 


{ 


    // Default smallest Positive Integer 


    int m = 1; 


  


    // Store values in set which are 


    // greater than variable m 


    HashSet<int> x = new HashSet<int>(); 


  


    for (int i = 0; i < n; i++) 


    { 


        // Store value when m is less than 


        // current index of given array 


        if (m < arr[i]) 


        { 


            x.Add(arr[i]); 


        } 


          


        else if (m == arr[i]) 


        { 


            // Increment m when it is equal 


            // to current element 


            m = m + 1; 


  


            while (x.Contains(m))  


            { 


                x.Remove(m); 


  


                // Increment m when it is one of the 


                // element of the set 


                m = m + 1; 


            } 


        } 


    } 


  


    // Return the required answer 


    return m; 


} 


  


// Driver code 


public static void Main(String[] args)  


{ 


    int []arr = { 2, 3, -7, 6, 8, 1, -10, 15 }; 


  


    int n = arr.Length; 


  


    // Function call 


    Console.WriteLine(findMissingPositive(arr, n)); 


} 


} 


  


// This code is contributed by Rajput-Ji 



















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Output:


4







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