[알고리즘문제풀기] 등차수열의 특정한 항만 더하기

문제

내가 작성한 정답

for

class Solution {
    public int solution(int a, int d, boolean[] included) {
        int answer = 0;
        for(int i=0; i<included.length; i++){
            if(included[i]) answer += a+i*d; 
        }
        return answer;
    }
}

stream

import java.util.stream.IntStream;

class Solution {
    public int solution(int a, int d, boolean[] included) {
        return IntStream.range(0,included.length)
                .filter(i->included[i])
                .map(i->a+i*d)
                .sum();
    }
}

다른 사람들의 정답

class Solution {
    public int solution(int a, int d, boolean[] included) {
        return IntStream.range(0, included.length)
                .map(idx -> included[idx]?a+(idx*d):0)
                .sum();
    }
}