[codility]Lesson 6 Sorting - Distinct

https://app.codility.com/programmers/lessons/6-sorting/distinct/

Distinct coding task - Learn to Code - Codility

Write a function

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

that, given an array A consisting of N integers, returns the number of distinct values in array A.

For example, given array A consisting of six elements such that:

 A[0] = 2    A[1] = 1    A[2] = 1
 A[3] = 2    A[4] = 3    A[5] = 1
the function should return 3, because there are 3 distinct values appearing in array A, namely 1, 2 and 3.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [0..100,000];
each element of array A is an integer within the range [−1,000,000..1,000,000].
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배열 A에서 중복된 값을 제거하고 남은 값의 길이를 리턴하는 문제 입니다.

 

// 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 8
        HashMap result = new HashMap();
        for(int b : A){
            result.put(b,b);
        }    
    
        return result.size();        
    }
}

HashMap을 사용하였습니다. HashMap은 중복된 key값을 허용하지 않습니다.

비슷하게 HashSet을 사용할 수도 있는데 HashSet은 중복된 value값을 허용하지 않습니다.

 

 

 

다른 방법으로 Stream을 사용해 봤습니다.

 

// 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 8
          int [] result = Arrays.stream(A).distinct().toArray();
          return result.length;
    }
}

Performance tests에서 Timeout error에 걸리네요. 

stream으로 사용하는 방법이 성능면에서는 조금 더 안좋은 것 같습니다.