당구 연습 (연습문제)

원본 : https://school.programmers.co.kr/learn/courses/30/lessons/169198

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풀이

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

class Solution {
    public int[] solution(int m, int n, int startX, int startY, int[][] balls) {
        int[] answer = new int[balls.length];
        int i = 0;

        for (int[] ball : balls) {
            int[] upReflectBall = new int[]{ball[0], n - ball[1] + n};
            int[] downReflectBall = new int[]{ball[0], -ball[1]};
            int[] leftReflectBall = new int[]{-ball[0], ball[1]};
            int[] rightReflectBall = new int[]{m - ball[0] + m, ball[1]};

            List<Integer> distanceList = new ArrayList<>();

            int upReflectDistance = (int) (Math.pow(startX - upReflectBall[0], 2) + Math.pow(startY - upReflectBall[1], 2));
            int downReflectDistance = (int) (Math.pow(startX - downReflectBall[0], 2) + Math.pow(startY - downReflectBall[1], 2));
            int rightReflectDistance = (int) (Math.pow(startX - rightReflectBall[0], 2) + Math.pow(startY - rightReflectBall[1], 2));
            int leftReflectDistance = (int) (Math.pow(startX - leftReflectBall[0], 2) + Math.pow(startY - leftReflectBall[1], 2));

            if (startX != ball[0]) {
                distanceList.add(upReflectDistance);
                distanceList.add(downReflectDistance);

                if (startY == ball[1] && startX > ball[0]) {
                    distanceList.add(rightReflectDistance);
                }

                if (startY == ball[1] && startX < ball[0]) {
                    distanceList.add(leftReflectDistance);
                }
            }

            if (startY != ball[1]) {
                distanceList.add(leftReflectDistance);
                distanceList.add(rightReflectDistance);

                if (startX == ball[0] && startY > ball[1]) {
                    distanceList.add(upReflectDistance);
                }

                if (startX == ball[0] && startY < ball[1]) {
                    distanceList.add(downReflectDistance);
                }
            }

            if (startY - ball[1] / startX - ball[0] == m / n) {
                int[] upRigthReflectBall = new int[]{m - ball[0] + m, n - ball[1] + n};
                int[] downLeftReflectBall = new int[]{-ball[0], -ball[1]};

                distanceList.add((int) (Math.pow(upRigthReflectBall[0] - startX, 2) + Math.pow(upRigthReflectBall[1] - startY, 2)));
                distanceList.add((int) (Math.pow(downLeftReflectBall[0] - startX, 2) + Math.pow(downLeftReflectBall[1] - startY, 2)));
            } else if (startY - ball[1] / startX - ball[0] == -m / n) {
                int[] upLeftReflectBall = new int[]{-ball[0], n - ball[1] + n};
                int[] downRightReflectBall = new int[]{m - ball[0] + m, -ball[1]};

                distanceList.add((int) (Math.pow(upLeftReflectBall[0] - startX, 2) + Math.pow(upLeftReflectBall[1] - startY, 2)));
                distanceList.add((int) (Math.pow(downRightReflectBall[0] - startX, 2) + Math.pow(downRightReflectBall[1] - startY, 2)));
            }

            distanceList.sort(null);

            answer[i++] = distanceList.get(0);
        }

        return answer;
    }
}