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Swift Programming: The Big Nerd Ranch Guide by John Gallagher, Matthew Mathias

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Platinum Challenge

Point’s current conformance to Comparable yields some confusing results.

let c = Point(x: 3, y: 4)
let d = Point(x: 2, y: 5)

let cGreaterThanD = (c > d) // false
let cLessThanD = (c < d)    // false
let cEqualToD = (c == d)    // false

As the above example demonstrates, the trouble arises in comparing two points when one point’s x and y properties are not both larger than the other point’s. In actuality, it is not reasonable to compare two points in this manner.

Fix this problem by changing Point’s conformance to Comparable. Calculate each point’s Euclidean distance from the origin instead of comparing x and y values. This implementation should return true for a < b when a is closer to the origin than b.

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