Day 19. 코딩 기초 트레이닝(Java)

1. 세 개의 구분자

https://school.programmers.co.kr/learn/courses/30/lessons/181862

프로그래머스

▼ 방법 1

import java.util.List;
import java.util.ArrayList;

class Solution {
    public String[] solution(String myStr) {
        String[] answer = {};
        String[] splitArr = myStr.replaceAll("a|b|c", " ").split(" ");
        List<String> answerList = new ArrayList<>();
        
        for(int i = 0; i < splitArr.length; i++) {
            if(!splitArr[i].isEmpty()) {
                answerList.add(splitArr[i]);
            }
        }
        
        answer = answerList.stream().toArray(String[]::new);
        answer = answer.length > 0 ? answer : new String[] {"EMPTY"};
        
        return answer;
    }
}

 

▼ 방법 2

import java.util.Arrays;

class Solution {
    public String[] solution(String myStr) {
        String[] answer = {};
        
        answer = Arrays.stream(myStr.split("[abc]+")).filter(s -> !s.isEmpty()).toArray(String[]::new);
        answer = answer.length > 0 ? answer : new String[] {"EMPTY"};
        
        return answer;
    }
}

 

2. 배열의 원소만큼 추가하기

https://school.programmers.co.kr/learn/courses/30/lessons/181861

프로그래머스

▼ 방법 1

import java.util.List;
import java.util.ArrayList;

class Solution {
    public int[] solution(int[] arr) {
        int[] answer = {};
        List<Integer> answerList = new ArrayList<>();
        
        for(int i = 0; i < arr.length; i++) {
            for(int j = 0; j < arr[i]; j++) {
                answerList.add(arr[i]);
            }
        }
        
        answer = answerList.stream().mapToInt(Integer::new).toArray();
        
        return answer;
    }
}

 

▼ 방법 2

import java.util.Arrays;

class Solution {
    public int[] solution(int[] arr) {
        int[] answer = new int[Arrays.stream(arr).sum()];
        int idx = 0;
        
        for(int n : arr) {
            for(int i = 0; i < n; i++) {
                answer[idx++] = n;
            }
        }
        
        return answer;
    }
}

 

▼ 방법 3

import java.util.stream.Stream;

class Solution {
    public int[] solution(int[] arr) {
        int[] answer = {};
        String str = "";
        
        for(int n : arr) {
            str += (String.valueOf(n) + ",").repeat(n);
        }
        
        answer = Stream.of(str.split(",")).mapToInt(Integer::parseInt).toArray();
        
        return answer;
    }
}

 

3. 빈 배열에 추가, 삭제하기

https://school.programmers.co.kr/learn/courses/30/lessons/181860

프로그래머스

▼ 방법 1

import java.util.List;
import java.util.ArrayList;

class Solution {
    public int[] solution(int[] arr, boolean[] flag) {
        int[] answer = {};
        List<Integer> answerList = new ArrayList<>();
        
        for(int i = 0; i < arr.length; i++) {
            if(flag[i]) {
                for(int j = 0; j < arr[i] * 2; j++) {
                    answerList.add(arr[i]);
                }
            } else {
                for(int j = 0; j < arr[i]; j++) {
                    answerList.remove(answerList.size() - 1);
                }
            }
        }
        
        answer = answerList.stream().mapToInt(Integer::new).toArray();
        
        return answer;
    }
}

 

▼ 방법 2

import java.util.Stack;

class Solution {
    public int[] solution(int[] arr, boolean[] flag) {
        int[] answer = {};
        Stack<Integer> answerStack = new Stack<>();
        
        for(int i = 0; i < arr.length; i++) {
            if(flag[i]) {
                for(int j = 0; j < arr[i] * 2; j++) {
                    answerStack.push(arr[i]);
                }
            } else {
                for(int j = 0; j < arr[i]; j++) {
                    answerStack.pop();
                }
            }
        }
        
        answer = answerStack.stream().mapToInt(Integer::new).toArray();
        
        return answer;
    }
}

 

▼ 방법 3

import java.util.stream.Stream;

class Solution {
    public int[] solution(int[] arr, boolean[] flag) {
        int[] answer = {};
        String answerStr = "";
        
        for(int i = 0; i < arr.length; i++) {
            if(flag[i]) {
                answerStr += String.valueOf(arr[i]).repeat(arr[i] * 2);
            } else {
                answerStr = answerStr.substring(0, answerStr.length() - arr[i]);
            }
        }
        
        answer = Stream.of(answerStr.split("")).mapToInt(Integer::parseInt).toArray();
        
        return answer;
    }
}

 

4. 배열 만들기 6

https://school.programmers.co.kr/learn/courses/30/lessons/181859

프로그래머스

▼ 방법 1

import java.util.List;
import java.util.ArrayList;

class Solution {
    public int[] solution(int[] arr) {
        int[] answer = {};
        List<Integer> answerList = new ArrayList<>();
        
        for(int i = 0; i < arr.length; i++) {
            if(answerList.size() == 0 || answerList.get(answerList.size() - 1) != arr[i]) {
                answerList.add(arr[i]);
            } else {
                answerList.remove(answerList.size() - 1);
            }
        }
        
        answer = answerList.size() == 0 ? new int[] {-1} : answerList.stream().mapToInt(Integer::new).toArray();
        
        return answer;
    }
}

 

▼ 방법 2

import java.util.Stack;

class Solution {
    public int[] solution(int[] arr) {
        int[] answer = {};
        Stack<Integer> answerStack = new Stack<>();
        
        for(int i = 0; i < arr.length; i++) {
            if(answerStack.isEmpty() || answerStack.peek() != arr[i]) {
                answerStack.push(arr[i]);
            } else {
                answerStack.pop();
            }
        }
        
        answer = answerStack.isEmpty() ? new int[] {-1} : answerStack.stream().mapToInt(Integer::new).toArray();
        
        return answer;
    }
}

push(Element item) : 데이터 추가
pop() : 최근에 추가된(Top) 데이터 삭제
peek() : 최근에 추가된(Top) 데이터 조회

 

5. 무작위로 K개의 수 뽑기

https://school.programmers.co.kr/learn/courses/30/lessons/181858

프로그래머스

▼ 방법 1

import java.util.List;
import java.util.ArrayList;

class Solution {
    public int[] solution(int[] arr, int k) {
        int[] answer = {};
        List<Integer> answerList = new ArrayList<>();
        
        for(int i = 0; i < arr.length; i++) {
            if(!answerList.contains(arr[i])) {
                answerList.add(arr[i]);
            }
            
            if(answerList.size() == k) {
                break;
            }
        }
        
        while(answerList.size() < k) {
            answerList.add(-1);
        }
        
        answer = answerList.stream().mapToInt(Integer::new).toArray();
        
        return answer;
    }
}

 

▼ 방법 2

import java.util.stream.IntStream;
import java.util.Arrays;

class Solution {
    public int[] solution(int[] arr, int k) {
        int[] answer = {};
        
        arr = IntStream.of(arr).distinct().toArray();
        answer = Arrays.copyOf(arr, k);
        
        if(arr.length < k) {
            Arrays.fill(answer, arr.length, k, -1);
        }
        
        return answer;
    }
}

Arrays.fill(배열 변수, 초기화할 값) : 배열 전체를 특정 값으로 채울 때 사용한다.
Arrays.fill(배열 변수, 시작, 끝+1, 초기화할 값) : 배열 전체가 아니라 구간을 지정하여 특정 값으로 채울 때 사용한다.

 

▼ 방법 3

import java.util.stream.IntStream;
import java.util.Arrays;

class Solution {
    public int[] solution(int[] arr, int k) {
        int[] answer = {};
        
        answer = IntStream.concat(Arrays.stream(arr).distinct(), IntStream.range(0, k).map(i -> -1)).limit(k).toArray();
        
        return answer;
    }
}