Problem no. 41.java

// Ques : First missing positive
// Ques Link : https://leetcode.com/problems/first-missing-positive/ 


package com.nitin;

public class FirstMissingPositive {
    public static void main(String[] args) {
        int[] arr = {3, 4, -1, 1};
        System.out.println(firstMissingPositive(arr));
    }

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

        for (int index = 0; index < arr.length; index++) {
            if (arr[index] != index + 1) {
                return index + 1;
            }
        }
        return arr.length + 1;
    }

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