# Smallest Positive missing number in Java

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:

1. Create a new HashMap to store positive integers in the array.
2. Loop through the array, and for each positive integer in the array, insert it as a key in the HashMap.
3. 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.
4. 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)
{
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 GeeksforGeeksCodesagar only provides a solution for it. This solution is only for Educational and learning purposes.