Circles of given radius through two points: Difference between revisions

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@@ Line 3,383: / Line 3,383: @@
 |  .9876   .9876  |
     +-----------------+</lang>
+=={{header|Swift}}==
+{{trans|F#}}
+<lang swift>import Foundation
+struct Point: Equatable {
+    var x: Double
+    var y: Double
+}
+struct Circle {
+  var center: Point
+  var radius: Double
+  public static func circleBetween(
+    _ p1: Point,
+    _ p2: Point,
+    withRadius radius: Double
+  ) -> (Circle, Circle?)? {
+    func applyPoint(_ p1: Point, _ p2: Point, op: (Double, Double) -> Double) -> Point {
+      return Point(x: op(p1.x, p2.x), y: op(p1.y, p2.y))
+    }
+    func mul2(_ p: Point, mul: Double) -> Point {
+      return Point(x: p.x * mul, y: p.y * mul)
+    }
+    func div2(_ p: Point, div: Double) -> Point {
+      return Point(x: p.x / div, y: p.y / div)
+    }
+    func norm(_ p: Point) -> Point {
+      return div2(p, div: (p.x * p.x + p.y * p.y).squareRoot())
+    }
+    guard radius != 0, p1 != p2 else {
+      return nil
+    }
+    let diameter = 2 * radius
+    let pq = applyPoint(p1, p2, op: -)
+    let magPQ = (pq.x * pq.x + pq.y * pq.y).squareRoot()
+    guard diameter >= magPQ else {
+      return nil
+    }
+    let midpoint = div2(applyPoint(p1, p2, op: +), div: 2)
+    let halfPQ = magPQ / 2
+    let magMidC = abs(radius * radius - halfPQ * halfPQ).squareRoot()
+    let midC = mul2(norm(Point(x: -pq.y, y: pq.x)), mul: magMidC)
+    let center1 = applyPoint(midpoint, midC, op: +)
+    let center2 = applyPoint(midpoint, midC, op: -)
+    if center1 == center2 {
+      return (Circle(center: center1, radius: radius), nil)
+    } else {
+      return (Circle(center: center1, radius: radius), Circle(center: center2, radius: radius))
+    }
+  }
+}
+let testCases = [
+  (Point(x: 0.1234, y: 0.9876), Point(x: 0.8765, y: 0.2345), 2.0),
+  (Point(x: 0.0000, y: 2.0000), Point(x: 0.0000, y: 0.0000), 1.0),
+  (Point(x: 0.1234, y: 0.9876), Point(x: 0.1234, y: 0.9876), 2.0),
+  (Point(x: 0.1234, y: 0.9876), Point(x: 0.8765, y: 0.2345), 0.5),
+  (Point(x: 0.1234, y: 0.9876), Point(x: 0.1234, y: 0.9876), 0.0)
+]
+for testCase in testCases {
+  switch Circle.circleBetween(testCase.0, testCase.1, withRadius: testCase.2) {
+  case nil:
+    print("No ans")
+  case (let circle1, nil)?:
+    print("One ans: \(circle1)")
+  case (let circle1, let circle2?)?:
+    print("Two ans: \(circle1) \(circle2)")
+  }
+}
+</lang>
+{{out}}
+<pre>Two ans: Circle(center: Point(x: -0.8632118016581896, y: -0.7521118016581892), radius: 2.0) Circle(center: Point(x: 1.8631118016581893, y: 1.974211801658189), radius: 2.0)
+One ans: Circle(center: Point(x: 0.0, y: 1.0), radius: 1.0)
+No ans
+No ans
+No ans</pre>
 =={{header|Tcl}}==