Day 25. 코딩 기초 트레이닝(Java)

1. 정수를 나선형으로 배치하기

https://school.programmers.co.kr/learn/courses/30/lessons/181832

프로그래머스

▼ 방법 1

class Solution {
    public int[][] solution(int n) {
        int[][] answer = new int[n][n];
        int num = 1;
        int rowStart = 0;
        int rowEnd = n - 1;
        int colStart = 0;
        int colEnd = n - 1;
        
        while(rowStart <= rowEnd && colStart <= colEnd) {
            for(int i = colStart; i <= colEnd; i++) {
                answer[rowStart][i] = num++;
            }
            
            rowStart++;
            
            for(int i = rowStart; i <= rowEnd; i++) {
                answer[i][colEnd] = num++;
            }
            
            colEnd--;
            
            for(int i = colEnd; i >= colStart; i--) {
                answer[rowEnd][i] = num++;
            }
            
            rowEnd--;
            
            for(int i = rowEnd; i >= rowStart; i--) {
                answer[i][colStart] = num++;
            }
            
            colStart++;
        }
        
        return answer;
    }
}

 

▼ 방법 2

class Solution {
    public int[][] solution(int n) {
        int[][] answer = new int[n][n];
        int num = 1;
        int x = 0, y = 0;
        int[] dx = {0, 1, 0, -1};
        int[] dy = {1, 0, -1, 0};
        int direction = 0;
        
        while(num <= n * n) {
            answer[x][y] = num++;
            
            int nx = x + dx[direction];
            int ny = y + dy[direction];
            
            if(nx < 0 || nx >= n || ny < 0 || ny >= n || answer[nx][ny] != 0) {
                direction = (direction + 1) % 4;
                nx = x + dx[direction];
                ny = y + dy[direction];
            }
            
            x = nx;
            y = ny;
        }
        
        return answer;
    }
}

 

2. 특별한 이차원 배열 2

https://school.programmers.co.kr/learn/courses/30/lessons/181831

프로그래머스

▼ 방법 1

class Solution {
    public int solution(int[][] arr) {
        int answer = 1;
        
        for(int i = 0; i < arr.length; i++) {
            for(int j = 0; j < arr[i].length; j++) {
                if(arr[i][j] != arr[j][i]) {
                    answer = 0;
                    
                    break;
                }
            }
        }
        
        return answer;
    }
}

 

▼ 방법 2

import java.util.stream.IntStream;

class Solution {
    public int solution(int[][] arr) {
        int answer = 0;
        
        answer = IntStream.range(0, arr.length).allMatch(i -> IntStream.range(0, arr[0].length).allMatch(j -> arr[i][j] == arr[j][i])) ? 1 : 0;
        
        return answer;
    }
}

 

3. 정사각형으로 만들기

https://school.programmers.co.kr/learn/courses/30/lessons/181830

프로그래머스

▼ 방법 1

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

 

▼ 방법 2

class Solution {
    public int[][] solution(int[][] arr) {
        int max = Math.max(arr.length, arr[0].length);
        int[][] answer = new int[max][max];
        
        for(int i = 0; i < arr.length; i++) {
            System.arraycopy(arr[i], 0, answer[i], 0, arr[i].length);
        }
        
        return answer;
    }
}

System.arraycopy()
Java Native Interface를 사용하기 때문에 clone()보다 더 빠르다.

System.arraycopy( A, sourcePos, B, destPos, len );
- Object A : 복사할 대상
- int sourcePos : 복사할 배열(A)의 시작 index
- Object B : 복사될 대상
- int destPos : 복사될 곳(B)의 시작 index
- int len : 복사할 길이(원소 개수)

 

4. 이차원 배열 대각선 순회하기

https://school.programmers.co.kr/learn/courses/30/lessons/181829

프로그래머스

▼ 방법 1

class Solution {
    public int solution(int[][] board, int k) {
        int answer = 0;
        
        for(int i = 0; i < board.length; i++) {
            if(i > k) {
                break;
            }
            
            for(int j = 0; j < board[i].length; j++) {
                if(i + j <= k) {
                    answer += board[i][j];
                }
            }
        }
        
        return answer;
    }
}

 

▼ 방법 2

import java.util.stream.IntStream;

class Solution {
    public int solution(int[][] board, int k) {
        int answer = 0;
        
        answer = IntStream.range(0, board.length).filter(i -> i <= k).map(i -> IntStream.range(0, board[i].length).filter(j -> i + j <= k).map(j -> board[i][j]).sum()).sum();
        
        return answer;
    }
}