FirstMissingPositive.java

// First Missing Positive
// URL : https://leetcode.com/problems/first-missing-positive/

package com.akshat;

public class FirstMissingPositive {

    public static void main(String[] args) {

        int[] nums = {7, 8, 9, 11, 12};

        System.out.println(firstMissingPositive(nums));

    }

    static int firstMissingPositive(int[] nums){
        int i = 0;
        while (i < nums.length){
            int correct = nums[i] - 1;
            if (nums[i]>0 && nums[i]<=nums.length && nums[i]!=nums[correct]){
                swap(nums, i, correct);
            }
            else{
                i++;
            }
        }
        for (int index=0; index< nums.length; index++){
            if (nums[index] != index+1){
                return index+1;
            }
        }
        return nums.length+1;
    }

    static void swap(int[] nums, int first, int second){
        int temp = nums[first];
        nums[first] = nums[second];
        nums[second] = temp;
    }

}