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Task/Problem-of-Apollonius/Swift/problem-of-apollonius.swift

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+import Foundation
+
+struct Circle {
+    let center:[Double]!
+    let radius:Double!
+
+    init(center:[Double], radius:Double) {
+        self.center = center
+        self.radius = radius
+    }
+
+    func toString() -> String {
+        return "Circle[x=\(center[0]),y=\(center[1]),r=\(radius)]"
+    }
+}
+
+func solveApollonius(c1:Circle, c2:Circle, c3:Circle,
+    s1:Double, s2:Double, s3:Double) -> Circle {
+
+        let x1 = c1.center[0]
+        let y1 = c1.center[1]
+        let r1 = c1.radius
+        let x2 = c2.center[0]
+        let y2 = c2.center[1]
+        let r2 = c2.radius
+        let x3 = c3.center[0]
+        let y3 = c3.center[1]
+        let r3 = c3.radius
+
+        let v11 = 2*x2 - 2*x1
+        let v12 = 2*y2 - 2*y1
+        let v13 = x1*x1 - x2*x2 + y1*y1 - y2*y2 - r1*r1 + r2*r2
+        let v14 = 2*s2*r2 - 2*s1*r1
+
+        let v21 = 2*x3 - 2*x2
+        let v22 = 2*y3 - 2*y2
+        let v23 = x2*x2 - x3*x3 + y2*y2 - y3*y3 - r2*r2 + r3*r3
+        let v24 = 2*s3*r3 - 2*s2*r2
+
+        let w12 = v12/v11
+        let w13 = v13/v11
+        let w14 = v14/v11
+
+        let w22 = v22/v21-w12
+        let w23 = v23/v21-w13
+        let w24 = v24/v21-w14
+
+        let P = -w23/w22
+        let Q = w24/w22
+        let M = -w12*P-w13
+        let N = w14 - w12*Q
+
+        let a = N*N + Q*Q - 1
+        let b = 2*M*N - 2*N*x1 + 2*P*Q - 2*Q*y1 + 2*s1*r1
+        let c = x1*x1 + M*M - 2*M*x1 + P*P + y1*y1 - 2*P*y1 - r1*r1
+
+        let D = b*b-4*a*c
+
+        let rs = (-b - sqrt(D)) / (2*a)
+        let xs = M + N * rs
+        let ys = P + Q * rs
+
+        return  Circle(center: [xs,ys], radius: rs)
+
+}
+
+let c1 = Circle(center: [0,0], radius: 1)
+let c2 = Circle(center: [4,0], radius: 1)
+let c3 = Circle(center: [2,4], radius: 2)
+
+println(solveApollonius(c1,c2,c3,1,1,1).toString())
+println(solveApollonius(c1,c2,c3,-1,-1,-1).toString())