Day 08 - 코딩테스트 입문(Java)

1. 배열 자르기

https://school.programmers.co.kr/learn/courses/30/lessons/120833

프로그래머스

▼ 방법 1

class Solution {
    public int[] solution(int[] numbers, int num1, int num2) {
        int[] answer = new int[num2 - num1 + 1];
        
        for(int i = num1; i <= num2; i++) {
            answer[i - num1] = numbers[i];
        }
        
        return answer;
    }
}

 

▼ 방법 2

import java.util.stream.IntStream;

class Solution {
    public int[] solution(int[] numbers, int num1, int num2) {
        int[] answer = {};
        
        answer = IntStream.rangeClosed(num1, num2).map(i -> numbers[i]).toArray();
        
        return answer;
    }
}

 

▼ 방법 3

import java.util.Arrays;

class Solution {
    public int[] solution(int[] numbers, int num1, int num2) {
        int[] answer = {};
        
        answer = Arrays.copyOfRange(numbers, num1, num2 + 1);
        
        return answer;
    }
}

 

2. 외계행성의 나이

https://school.programmers.co.kr/learn/courses/30/lessons/120834

프로그래머스

▼ 방법 1

class Solution {
    public String solution(int age) {
        String answer = "";
        char[] alphabet = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'};
        
        while(age >= 1) {
            answer = alphabet[age % 10] + answer;
            age /= 10;
        }
        
        return answer;
    }
}

 

▼ 방법 2

class Solution {
    public String solution(int age) {
        String answer = "";
        
        while(age >= 1) {
            answer = (char) (age % 10 + 'a') + answer;
            age /= 10;
        }
        
        return answer;
    }
}

 

▼ 방법 3

class Solution {
    public String solution(int age) {
        String answer = "";
        
        for(int i = 0; i < String.valueOf(age).length(); i++) {
            answer += (char) (String.valueOf(age).charAt(i) + ('a' - '0'));
        }
        
        return answer;
    }
}

 

▼ 방법 4

import java.util.stream.Collectors;

class Solution {
    public String solution(int age) {
        String answer = "";
        
        answer = String.valueOf(age).chars().mapToObj(c -> String.valueOf((char) (c + ('a' - '0')))).collect(Collectors.joining());
        
        return answer;
    }
}

 

3. 진료순서 정하기

https://school.programmers.co.kr/learn/courses/30/lessons/120835

프로그래머스

▼ 방법 1

import java.util.Arrays;

class Solution {
    public int[] solution(int[] emergency) {
        int[] answer = new int[emergency.length];
        int[] emergencySort = emergency.clone();
        
        Arrays.sort(emergencySort);
        
        for(int i = 0; i < emergency.length; i++) {
            for(int j = 0; j < emergencySort.length; j++) {
                if(emergency[i] == emergencySort[j]) {
                    answer[i] = emergency.length - j;

                    break;
                }
            }
        }
        
        return answer;
    }
}

 

▼ 방법 2

class Solution {
    public int[] solution(int[] emergency) {
        int[] answer = new int[emergency.length];
        
        for(int i = 0; i < emergency.length; i++) {
            answer[i]++;
            
            for(int j = 0; j < emergency.length; j++) {
                if(emergency[i] < emergency[j]) {
                    answer[i]++;
                }
            }
        }
        
        return answer;
    }
}

 

▼ 방법 3

import java.util.Arrays;
import java.util.Comparator;
import java.util.stream.Collectors;

class Solution {
    public int[] solution(int[] emergency) {
        int[] answer = {};
        
        answer = Arrays.stream(emergency).map(i -> Arrays.stream(emergency).boxed().sorted(Comparator.reverseOrder()).collect(Collectors.toList()).indexOf(i) + 1).toArray();
        
        return answer;
    }
}

 

4. 순서쌍의 개수

https://school.programmers.co.kr/learn/courses/30/lessons/120836

프로그래머스

▼ 방법 1

class Solution {
    public int solution(int n) {
        int answer = 0;
        
        for(int i = 1; i <= n; i++) {
            if(n % i == 0) {
                answer++;
            }
        }
        
        return answer;
    }
}

 

▼ 방법 2

import java.util.stream.IntStream;

class Solution {
    public int solution(int n) {
        int answer = 0;
        
        answer = (int) IntStream.rangeClosed(1, n).filter(i -> n % i == 0).count();
        
        return answer;
    }
}