MissingInteger.java

// you can also use imports, for example:
// import java.util.*;

// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");

import java.util.Arrays;

class Solution {
    public int solution(int[] A) {
        // write your code in Java SE 8
        Arrays.sort(A);
        
        if (A[A.length - 1] < 1) {
            return 1;
        }


        for (int i = 0; i < A.length; i ++) {
            if (i == 0) {
                continue;
            }

            if (A[i] == A[i - 1]) {
                continue;
            }

            if (A[i] == A[i - 1] + 1) {
                continue;
            } else {
                return A[i - 1] + 1;
            }
            
        }

        return A[A.length - 1] + 1;
    }

    public static void main(String [] args) {
        Solution sol = new Solution();

        System.out.println(sol.solution(new int[] {2}));
        System.out.println(sol.solution(new int[] {1, 3, 6, 4, 1, 2}));
        System.out.println(sol.solution(new int[] {1,2,3}));
        System.out.println(sol.solution(new int[] {-1, -3}));

        int[] arr = new int[100000];
        for (int a = 0; a < 100000; a++) {

            arr[a] = 100 + a;
        }

        arr[1000] = 1000000;
        System.out.println(arr[arr.length - 1]);
        System.out.println(sol.solution(arr));
        // for ( int a = 0; a < 100000; a++ ) {
        //     System.out.println(a);
        // }
    }
}