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Decode the Coding Interview in Java: Real-World Examples

Angle Between the Hands of a Clock

Understand how to calculate the smaller angle between the hour and minute hands of a clock given any time. Learn to compute individual angles for each hand based on hours and minutes, then find the minimal difference. This lesson helps you apply basic math and modular operations in Java with efficient O(1) time and space complexity.

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Description

Given two numbers, hour and minutes we will return the smaller angle (in degrees) formed between the hour and the minute hands on a clock.

Let’s look at some examples to better understand this:

Coding exercise

Java
class Solution {
  public static double clockAngle(int hour, int minutes) {
    // Your code goes here
    
    return 0.1; // Change the return value as per your requirement
  }
}
Angle between hands of a clock

Solution

The idea is to separately calculate the angles between the 0-minutes vertical line and each hand. The answer will be the difference that is found between the two angles.

Note: Black lines in the clock represent the 0-minutes vertical lines.

Minute hand angle

Let’s start from the minute hand. The minute hand moves with 1 min intervals. At 1 min, the angle of the minute hand is 6°. . Since the whole circle of the clock is equal to 360° degrees and 60 minutes, we estimated that the minute hand moves 1 min = 360° / 60 = 6° degree with each minute.

Now, we can easily find an angle between the 0-minutes vertical line and a minute hand, using minutesAngle = minutes X 6°. ...