First Missing Positive

Given an unsorted integer array, find the smallest missing positive integer.

Example 1:

Input: [1,2,0]
Output: 3

 
Example 2:

Input: [3,4,-1,1]
Output: 2

 
Example 3:

Input: [7,8,9,11,12]
Output: 1 

import java.util.*;
class NewClass5 {

    HashMap<Integer,Integer> arr=new HashMap<Integer,Integer>();
  
    int Max(int nums[])
    {
         int max=nums[0];
        for(int i=0;i<nums.length;i++)
        {
            if(nums[i]>max)
                max=nums[i];
            arr.put(nums[i], 1);
        }
        return max;
    }
     void firstMissingPositive(int max) {
     
      
        for(int i=1;i<=max+1;i++)
        {
            if(!arr.containsKey(i)){
                System.out.println(i); break;}
        }
    }
     public static void main(String args[])
     {
         int ar[]={3,4,-1,1};
         NewClass5 ob=new NewClass5();
         int max=ob.Max(ar);
         ob.firstMissingPositive(max);
       
     }
}