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

Solutions to Chapter 10 | Mathematical
22 public double slope;
23 public double intercept;
24 private boolean infinite_slope = false;
25 public Line(GraphPoint p, GraphPoint q) {
26 if (Math.abs(p.x - q.x) > epsilon) { // if x’s are different
27 slope = (p.y - q.y) / (p.x - q.x); // compute slope
28 intercept = p.y - slope * p.x; // y intercept from y=mx+b
29 } else {
30 infinite_slope = true;
31 intercept = p.x; // x-intercept, since slope is infinite
32 }
33 }
34
35 public boolean isEqual(double a, double b) {
36 return (Math.abs(a - b) < epsilon);
37 }
38
39 @Override
40 public int hashCode() {
41 int sl = (int)(slope * 1000);
42 int in = (int)(intercept * 1000);
43 return sl | in;
44 }
45
46 @Override
47 public boolean equals(Object o) {
48 Line l = (Line) o;
49 if (isEqual(l.slope, slope) && isEqual(l.intercept, intercept)
50 && (infinite_slope == l.infinite_slope)) {
51 return true;
52 }
53 return false;
54 }
55 }
OBSERVATIONS AND SUGGESTIONS
»»
Be careful about the calculation of the slope of a line. The line might be completely
vertical. We can keep track of this in a separate flag (infinite_slope). We need to check
this condition in the equals method.
» » Remember that when we perform division to calculate the slope, division is not exact.
Therefore, rather than checking to see if two slopes are exactly equal, we need to check
if they’re different by greater than epsilon.
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