Smallest positive missing number

#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
Explanation: Smallest positive missing 
number is 6.



#Answer
#include<bits/stdc++.h>
using namespace std;


 // } Driver Code Ends


int findMissing(int arr[], int n){
    for(int i=0;i<n;i++){
        if(arr[abs(arr[i])-1] > 0 && (abs(arr[i])-1) < n)
            arr[abs(arr[i])-1] = - arr[abs(arr[i])-1];
    }
    for(int i=0;i<n;i++){
        if(arr[i]>0){
            return i+1;
        }
    }
    return n+1;
}
// Functio to find first smallest positive
// missing number in the array
int missingNumber(int arr[], int n) { 
    
    // Your code here
      int j=0;
    for(int i=0;i<n;i++){
        if(arr[i]<=0 || arr[i]>n){
            swap(arr[j],arr[i]);
            j++;
        }
    }
    return findMissing(arr+j,n-j);

    
} 

// { Driver Code Starts.

int missingNumber(int arr[], int n);

int main() { 
    int t;
    cin>>t;
    while(t--){
        int n;
        cin>>n;
        int arr[n];
        for(int i=0; i<n; i++)cin>>arr[i];
        cout<<missingNumber(arr, n)<<endl;
    }
    return 0; 
}   // } Driver Code Ends