Added lection 2.6

Author: Popov Valery

Lecture2_5.playground/playground.xcworkspace/xcuserdata/V.Popov.xcuserdatad/UserInterfaceState.xcuserstate

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+//: Playground - noun: a place where people can play
+
+import UIKit
+
+struct Rational: CustomStringConvertible {
+    
+    var numer: Int = 0
+    var denom: Int = 1
+    
+    var description: String {
+        let greatestCommonDivisior = gcd(numer, denom)
+        return "\(numer / greatestCommonDivisior)/\(denom / greatestCommonDivisior)"
+    }
+    
+    init?(numer: Int, denom: Int) {
+        
+        guard denom != 0 else {
+            return nil
+        }
+        
+        //assert(denom != 0)
+        
+        self.numer = numer
+        self.denom = denom
+    }
+    
+    init(value: Int) {
+        numer = value
+    }
+    
+    func add(r: Rational) -> Rational {
+        return Rational(numer: numer * r.denom + r.numer * denom, denom: r.denom * denom)!
+    }
+    
+    func sub(r: Rational) -> Rational {
+        return add(r.neg())
+    }
+    
+    func neg() -> Rational {
+        return Rational(numer: -numer, denom: denom)!
+    }
+    
+    func less(that: Rational) -> Bool {
+        return numer * that.numer < that.numer * denom
+    }
+    
+    func max(that: Rational) -> Rational {
+        return self.less(that) ? that : self
+    }
+    
+    
+    
+    private func gcd(a: Int, _ b: Int) -> Int {
+        return b == 0 ? a : gcd(b, a % b)
+    }
+}
+
+func +(left: Rational, right: Rational) -> Rational {
+    return Rational(numer: left.numer * right.denom + right.numer * left.denom,
+        denom: right.denom * left.denom)!
+}
+
+func -(left: Rational, right: Rational) -> Rational {
+    let negativeRight = right.neg()
+    return left + negativeRight
+}
+
+let a = Rational(numer: 24, denom: 6)
+
+let b = Rational(value: 4)
+

Lecture2_6.playground/Contents.swift

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Lecture2_6.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8"?>
+<Timeline
+   version = "3.0">
+   <TimelineItems>
+   </TimelineItems>
+</Timeline>