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Clock Angle in JavaScript

Problem

Given two integers, an hour and a minute, write a function to calculate the angle between the two hands on a clock representing that time.

Example 1:
Input: 3, 0
Output: 90
Example 2:
Input: 3, 20
Output: 20
Example 3:
Input: 12, 0
Output: 0
Example 4:
Input: 2, 45
Output: 172.5
Example 5:
Input: 9, 0
Output: 90

Approach

Find out the degree of angle per hour (360 / 12) and minute (360 / 60). Calculate the degree of angle for minute hand (minute * angle per minute). And then calcualte the degree of angle for hour hand (hour * angle per hour) plus the degree of angle made by minute hand (minute / 60 * angle per hour). Calculate the difference in degree of angle between hour and minute hands. Finally, return the lowest degree of angles. For example, return 90 degree of angle for 9:00 instead of 270.

Solution


/**
 * Calculate the clock angle
 * @param {Number} hour
 * @param {Number} minute
 * @return {Number}
 * @time comlexity: O(1)
 * @space complexity: O(1)
 */
const clockAngle = (hour, minute) => {
  const ANGLE_PER_HOUR = 360 / 12,
        ANGLE_PER_MINUTE = 360 / 60,
        minuteHand = minute * ANGLE_PER_MINUTE,
        hourHand = hour * ANGLE_PER_HOUR + minute / 60 * ANGLE_PER_HOUR;

  const angle = Math.abs(hourHand - minuteHand);

  return Math.min(360 - angle, angle);
};

Test Case


import { assert } from 'chai';

describe('Clock Angle', () => {

    it('3:00 should be 90 degree', () => {
      assert.strictEqual(clockAngle(3, 0), 90);
    });

    it('3:20 should be 20 degree', () => {
      assert.strictEqual(clockAngle(3, 20), 20);
    });

    it('12:00 should be 0 degree', () => {
      assert.strictEqual(clockAngle(12, 0), 0);
    });

    it('2:45 should be 172.5 degree', () => {
      assert.strictEqual(clockAngle(2, 45), 172.5);
    });
    
    it('9:00 should be 90 degree', () => {
      assert.strictEqual(clockAngle(9, 0), 90);
    });

});

  Clock Angle
    ✓ 3:00 should be 90 degree
    ✓ 3:20 should be 20 degree
    ✓ 12:00 should be 0 degree
    ✓ 2:45 should be 172.5 degree
    ✓ 9:00 should be 90 degree


  5 passing (156ms)


Mike Mai
Mike Mai   Brooklyn, New York
I am full-stack web developer, passionate about building world class web applications. Knowledge in designing, coding, testing, and debugging. I love to solve problems.