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++

// 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;
}

Java

// 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

Python3

# 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

C#

// 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

Javascript

<script>

// JavaScript program to find the smallest
// positive missing number

// Function to find the smallest
// positive missing number
function findMissingPositive(arr, n)
{
    // Default smallest Positive integer
    let m = 1;

    // Store values in set which are
    // greater than variable m
    let x = new Set();

    for (let 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.has(m)) {
                x.delete(m);

                // Increment m when it is one of the
                // element of the set
                m = m + 1;
            }
        }
    }

    // Return the required answer
    return m;
}

// Driver code

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

let n = arr.length;

// Function call
document.write(findMissingPositive(arr, n));


// This code is contributed by _saurabh_jaiswal

</script>

Output:

4

Time Complexity: O(nlog(n))

Auxiliary Space: O(n)