You are given an array **arr**[] of **N** integers including 0. The task is to find the smallest positive number missing from the array.

**Example 1:**

Input:N = 5 arr[] = {1,2,3,4,5}Output:6

Here’s an algorithm for the missingNumber method:

- Create a new HashMap to store positive integers in the array.
- Loop through the array, and for each positive integer in the array, insert it as a key in the HashMap.
- Loop through integers from 1 to size:

a. Check if the current integer is present as a key in the HashMap. If it is not, return the integer. - If all integers from 1 to size are present in the HashMap, return size+1 as the smallest missing positive integer.

.

## Smallest Positive missing number in Java

class Solution { //Function to find the smallest positive number missing from the array. static int missingNumber(int arr[], int size) { // Your code here HashMap<Integer,Integer> hm=new HashMap<Integer,Integer>(); for(int i=0;i<size;i++){ if(arr[i]>0){ hm.put(arr[i],1); } } for(int i=1;i<=size;i++){ if(!hm.containsKey(i)) return i; } return size+1; } }

This Java code defines a class named `Solution`

that contains a static method named `missingNumber`

. This method takes two arguments: an array of integers `arr`

and an integer `size`

representing the size of the array. The method returns an integer representing the smallest positive number missing from the array.

The implementation of the `missingNumber`

method uses a `HashMap`

to keep track of the positive integers in the array. In the first loop, each positive integer in the array is inserted as a key into the `HashMap`

. The value associated with the key is not important, as we only care about whether or not the key exists in the `HashMap`

.

In the second loop, we check for the smallest positive integer missing from the array. We iterate over integers from 1 to `size`

and for each integer `i`

, we check if it is present as a key in the `HashMap`

. If it is not, then `i`

is the smallest positive integer missing from the array, and we return it.

If all integers from 1 to `size`

are present in the `HashMap`

, then the smallest missing positive integer must be `size + 1`

, which we return as the answer.

**Disclaimer:** This problem**(Smallest Positive Missing Number)** is originally created by GeeksforGeeks. Codesagar only provides a solution for it. This solution is only for Educational and learning purposes.