Cracking the Coding Interview - Fooo

Solutions to Chapter 10 | Mathematical
10 3 Given two lines on a Cartesian plane, determine whether the two lines would intersect
SOLUTION
1 8 9
Cracking the Coding Interview | Concepts and Algorithms
pg 68
There are a lot of unknowns in this problem (what format are the lines in? What if they are the
same line?), but let’s assume:
» If two lines are the same (same line = same slope and y-intercept), they are considered
to intersect
» We get to decide the data structure
1 public class Line {
2 static double epsilon = 0.000001;
3 public double slope;
4 public double yintercept;
5
6 public Line(double s, double y) {
7 slope = s;
8 yintercept = y;
9 }
10
11 public boolean intersect(Line line2) {
12 return Math.abs(slope - line2.slope) > epsilon ||
13 Math.abs(yintercept - line2.yintercept) < epsilon;
14 }
15 }
OBSERVATIONS AND SUGGESTIONS:
» Ask questions This question has a lot of unknowns—ask questions to clarify them Many
interviewers intentionally ask vague questions to see if you’ll clarify your assumptions
» When possible, design and use data structures It shows that you understand and care
about object oriented design
» Think through which data structures you design to represent a line There are a lot of
options, with lots of trade offs Pick one and explain your choice
» Don’t assume that the slope and y-intercept are integers
» Understand limitations of floating point representations Never check for equality with
==