Added new solutions with tests

Author: Michael-Ho-Bose

Easy/0007-ReverseInteger+0069-Sqrtx.playground/Contents.swift

@@ -1,26 +1,51 @@
 // LeetCode: https://leetcode.com/problems/reverse-integer/description/
+
 import Foundation
+import XCTest
 
 class Solution {
     func reverse(_ x: Int) -> Int {
         var temp = abs(x)
         var output = 0
         while temp > 0 {
-            var tail = temp % 10
+            output = output * 10 + temp % 10
             temp = temp / 10
-            output = output * 10 + tail
-            if (output > Int32.max || output < Int32.min) { return 0 }
         }
-        
-        return output * x.signum() // Times back the sign of the original number
+        guard output < Int32.max, output > Int32.min else { return 0 }
+        return output * x.signum()
     }
 
     func mySqrt(_ x: Int) -> Int {
         return Int(sqrt(Double(x)))
-        
     }
 }
 
-let solution = Solution()
-print("\(solution.reverse(-123))")
-print("\(solution.mySqrt(8))")
+class Tests: XCTestCase {
+    let solution = Solution()
+    
+    func testSample1() {
+        let input = -123
+        let expected = -321
+        XCTAssertEqual(solution.reverse(input), expected)
+    }
+    
+    func testSample2() {
+        let input = 123
+        let expected = 321
+            XCTAssertEqual(solution.reverse(input), expected)
+    }
+    
+    func testSample3() {
+        let input = 120
+        let expected = 21
+            XCTAssertEqual(solution.reverse(input), expected)
+    }
+    
+    func testSample4() {
+        let input = 1534236469
+        let expected = 0
+        XCTAssertEqual(solution.reverse(input), expected)
+    }
+}
+
+Tests.defaultTestSuite.run()

Medium/0017-LetterCombinationsOfAPhoneNumber.playground/Contents.swift

@@ -0,0 +1,44 @@
+// LeetCode: https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/
+
+class Solution {
+    func letterCombinations(_ digits: String) -> [String] {
+        var output: [String] = []
+        var dict = [
+            "2": "abc",
+            "3": "def",
+            "4": "ghi",
+            "5": "jkl",
+            "6": "mno",
+            "7": "pqrs",
+            "8": "tuv",
+            "9": "wxyz",
+            ]
+        for digit in digits {
+            if let str = dict[String(digit)] {
+                appendStr(output: &output, toAppend: str)
+            }
+        }
+        return output
+    }
+    
+    func appendStr(output: inout [String], toAppend: String) {
+        if output.count == 0 {
+            for str in toAppend {
+                output.append(String(str))
+            }
+            return
+        }
+        let temp = output
+        output = []
+        for str in toAppend {
+            var currentOut = temp
+            for index in 0..<currentOut.count {
+                currentOut[index].append(str)
+                output.append(currentOut[index])
+            }
+        }
+    }
+}
+
+let solution = Solution()
+print(solution.letterCombinations("23")) // ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]

Medium/0017-LetterCombinationsOfAPhoneNumber.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Medium/0238-ProductOfArrayExceptSelf.playground/Contents.swift

@@ -0,0 +1,42 @@
+// LeetCode: https://leetcode.com/problems/product-of-array-except-self/description/
+
+import XCTest
+
+class Solution {
+    func productExceptSelf(_ nums: [Int]) -> [Int] {
+        var zeroCount = 0
+        var sum = 1
+        for i in nums {
+            if i != 0 {
+                sum = sum * i
+            } else {
+                zeroCount += 1
+            }
+        }
+        if zeroCount > 1 {
+            return nums.map { _ in 0 }
+        } else if zeroCount == 1 {
+            return nums.map { $0 == 0 ? sum : 0 }
+        } else {
+            return nums.map { sum / $0 }
+        }
+    }
+}
+
+class Tests: XCTestCase {
+    let solution = Solution()
+    
+    func testSample1() {
+        let input = [1, 2, 3, 4]
+        let expected = [24, 12, 8, 6]
+        XCTAssertEqual(solution.productExceptSelf(input), expected)
+    }
+    
+    func testSample2() {
+        let input = [0, 0]
+        let expected = [0, 0]
+        XCTAssertEqual(solution.productExceptSelf(input), expected)
+    }
+}
+
+Tests.defaultTestSuite.run()

Medium/0238-ProductOfArrayExceptSelf.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos' executeOnSourceChanges='false'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Udacity Practices/Closures.playground/Contents.swift

@@ -0,0 +1,60 @@
+// Swift GCD
+
+// Assign to var or constant
+let f = { (x: Int) -> Int
+    in
+    return x + 42
+}
+
+f(9)
+f(76)
+
+// Closures in an array (or a dictionary, or a set, etc...)
+let closures = [
+    f,
+    {(x: Int) -> Int in return x * 2},
+    {x in return x - 8},
+    {x in x*x},
+    {$0 * 42}
+]
+// $0 means position zero
+
+for fn in closures {
+    fn(42)
+}
+
+// Functions and closures are exactly the same thing
+func foo(x: Int) -> Int {
+    return 42 + x
+}
+
+let foo = {(x: Int) -> Int
+    in
+    42 + x
+}
+
+foo(30)
+
+// MARK: - Typealias
+// Standard form: typealias newName = oldName
+typealias Integer = Int
+
+// Useful when used with functions and closures
+// (Int) -> Int
+typealias IntToInt = (Int) -> Int
+typealias IntMaker = () -> Int
+
+func makeCounter() -> IntMaker {
+    var n = 0
+    
+    func adder() -> Int {
+        n = n + 1
+        return n
+    }
+    
+    return adder
+}
+
+let counter1 = makeCounter()
+counter1()
+

Udacity Practices/Closures.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>