Cracking the Coding Interview, 4 Edition - 150 Programming Interview Questions and Solutions

Solutions to Chapter 10 | Mathematical
10.3 Given two lines on a Cartesian plane, determine whether the two lines would intersect.
SOLUTION
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:
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If two lines are the same (same line = same slope and y-intercept), they are considered
to intersect.
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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:
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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.
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When possible, design and use data structures. It shows that you understand and care
about object oriented design.
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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.
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Don’t assume that the slope and y-intercept are integers.
» » Understand limitations of floating point representations. Never check for equality with
==.
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Cracking the Coding Interview | Concepts and Algorithms