[SQL] [Codewars] 7kyu - Simple Fun #74: Growing Plant

 

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문제

Task

Each day a plant is growing by upSpeed meters. Each night that plant's height decreases by downSpeed meters due to the lack of sun heat. Initially, plant is 0 meters tall. We plant the seed at the beginning of a day. We want to know when the height of the plant will reach a certain level.

Example

For upSpeed = 100, downSpeed = 10 and desiredHeight = 910, the output should be 10.

After day 1 --> 100
After night 1 --> 90
After day 2 --> 190
After night 2 --> 180
After day 3 --> 280
After night 3 --> 270
After day 4 --> 370
After night 4 --> 360
After day 5 --> 460
After night 5 --> 450
After day 6 --> 550
After night 6 --> 540
After day 7 --> 640
After night 7 --> 630
After day 8 --> 730
After night 8 --> 720
After day 9 --> 820
After night 9 --> 810
After day 10 --> 910 

For upSpeed = 10, downSpeed = 9 and desiredHeight = 4, the output should be 1.

Because the plant reach to the desired height at day 1(10 meters).

After day 1 --> 10

더 자세한 내용은 홈페이지 참고.

 

코드

CREATE OR REPLACE FUNCTION plant(down int, up int, desired_height int)
RETURNS INTEGER AS $$
DECLARE
    day INTEGER := 0;
    height INTEGER := 0;
BEGIN
    WHILE height <= desired_height
    LOOP
        height := height + up;
        day := day + 1;
            IF height < desired_height THEN
                height := height - down;
            ELSE
                RETURN day;
            END IF;
    END LOOP;
    RETURN day;
END;
$$ LANGUAGE plpgsql;

SELECT
  id,
  plant(down_speed, up_speed, desired_height) as num_days
FROM growing_plant;

함수를 만들어서 풀었다.

 

더 쉽고 간단하게 하려면, 아래처럼 풀면 된다.

SELECT
  id, 
  CASE WHEN desired_height <= up_speed THEN 1
  ELSE CEIL((desired_height - up_speed)::decimal / (up_speed - down_speed))::int + 1 END AS num_days
FROM growing_plant;

 

설명

반복문을 활용하여 더하고 빼기를 반복하면 된다.