[Codillity] PermMissingElem

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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Solution

풀이

1. 해석

1부터 N까지의 숫자가 있는데 빠진 숫자를 구해라

 

2. 코드

// 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");

class Solution {
    public int solution(int[] A) {
        // write your code in Java SE 11
        Arrays.sort(A);
        
        for(int i = 0; i < A.length; i++) {
            if(A[i] != i+1)
                return i + 1;
        }
        return A.length + 1;
    }
}

• A 배열을 정렬한다
• 반복문을 돌면서 i번째 숫자가 i+1인지 확인한다.