[Codility] Time Complexity - PermMissingElem / Java

1. 문제

An array A consisting of N different integers is given. The array contains integers in the range [1..(N + 1)], which means that exactly one element is missing.

Your goal is to find that missing element.

Write a function:

class Solution { public int solution(int[] A); }

that, given an array A, returns the value of the missing element.

For example, given array A such that:

A[0] = 2 A[1] = 3 A[2] = 1 A[3] = 5

the function should return 4, as it is the missing element.

Write an efficient algorithm for the following assumptions:

• N is an integer within the range [0..100,000];
• the elements of A are all distinct;
• each element of array A is an integer within the range [1..(N + 1)].

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2. 코드

import java.util.*;

class Solution {
    public int solution(int[] A) {
        
        if(A.length == 0)
            return 1;
        
        Arrays.sort(A);
        
        for(int i=0; i<A.length; i++) {
            if(A[i] != i+1)
                return i+1;
        }
        
        return A[A.length-1] + 1;
    }
}