Push new solutions

Author: Michael Ho

Problems/1-100/Medium/0003-LongestSubstringWithoutRepeatingCharacters.playground/Contents.swift

@@ -5,26 +5,23 @@ import XCTest
 
 class Solution {
     func lengthOfLongestSubstring(_ s: String) -> Int {
-        let arr = Array(s)
-        var dict = [Character : Int]() // [char : idx]
+        guard s.count > 1 else { return s.count }
+        var dict: [Character: Int] = [:]
+        var startIdx = 0
         var maxCount = 0
-        var count = 0
-        for idx in 0..<arr.count {
-            if dict[arr[idx]] == nil {
-                count += 1
-                dict[arr[idx]] = idx
-            } else {
-                let startIdx = dict[arr[idx]]! + 1
-                dict[arr[idx]] = idx
-                for key in dict.keys {
-                    if dict[key]! < startIdx {
-                        dict[key] = nil
-                    }
-                }
-                count = idx - startIdx + 1
+        
+        for (i, ch) in s.enumerated() {
+            if let existIdx = dict[ch] {
+                startIdx = max(startIdx, existIdx)
             }
-            maxCount = max(count, maxCount)
+            
+            // Include the current one, exclude the existed one
+            maxCount = max(maxCount, i - startIdx + 1)
+            
+            // Make the index be excluded
+            dict[ch] = i + 1
         }
+        
         return maxCount
     }
 }
@@ -49,6 +46,12 @@ class Tests: XCTestCase {
         let expected = 3
         XCTAssertEqual(solution.lengthOfLongestSubstring(sample), expected)
     }
+    
+    func testSample4() {
+        let sample = "au"
+        let expected = 2
+        XCTAssertEqual(solution.lengthOfLongestSubstring(sample), expected)
+    }
 }
 
 Tests.defaultTestSuite.run()

Problems/1-100/Medium/0034-FindFirstandLastPositionElementSortedArray.playground/Contents.swift

@@ -0,0 +1,68 @@
+// LeetCode: https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/
+
+import XCTest
+
+class Solution {
+    func searchRange(_ nums: [Int], _ target: Int) -> [Int] {
+        var output = [-1, -1]
+        guard nums.count > 0 else { return output }
+        
+        if nums.count == 1 {
+            return target == nums[0] ? [0, 0] : output
+        }
+        
+        var start = 0
+        var end = nums.count - 1
+        while start <= end {
+            let mid = (start+end)/2
+            if target == nums[mid] {
+                output = [mid, mid]
+                break
+            } else if target < nums[mid] {
+                end = mid - 1
+            } else {
+                start = mid + 1
+            }
+        }
+        
+        while output[0] - 1 >= 0, nums[output[0] - 1] == target {
+            output[0] -= 1
+        }
+        
+        while output[1] + 1 < nums.count, nums[output[1] + 1] == target {
+            output[1] += 1
+        }
+        
+        return output
+    }
+}
+
+class Tests: XCTestCase {
+    let s = Solution()
+
+    func testSample1() {
+        let input = ([5,7,7,8,8,10], 8)
+        let expected = [3, 4]
+        XCTAssertEqual(expected, s.searchRange(input.0, input.1))
+    }
+
+    func testSample2() {
+        let input = ([5,7,7,8,8,10], 6)
+        let expected = [-1, -1]
+        XCTAssertEqual(expected, s.searchRange(input.0, input.1))
+    }
+    
+    func testSample3() {
+        let input = ([1], 1)
+        let expected = [0, 0]
+        XCTAssertEqual(expected, s.searchRange(input.0, input.1))
+    }
+    
+    func testSample4() {
+        let input = ([1, 4], 4)
+        let expected = [1, 1]
+        XCTAssertEqual(expected, s.searchRange(input.0, input.1))
+    }
+}
+
+Tests.defaultTestSuite.run()

Problems/1-100/Medium/0034-FindFirstandLastPositionElementSortedArray.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>

Problems/1-100/README.md

@@ -17,7 +17,7 @@ Straightforward solutions
 | # | Difficulty | Problem Title | Solution |
 |--| :--: | :--: | -- |
 | 0001 | 📗 | [Two Sum](https://leetcode.com/problems/two-sum/description/) | [Solution](https://github.com/twho/LeetCode-Swift/blob/master/Problems/1-100/Easy/0001-TwoSum.playground/Contents.swift) |
-| 0002 | 📙 | [Add Two Numbers](https://leetcode.com/problems/add-two-numbers/description/) | [Solution](https://github.com/twho/LeetCode-Swift/blob/master/Problems/1-100/0002-AddTwoNumbers.playground/Contents.swift) |
+| 0002 | 📙 | [Add Two Numbers](https://leetcode.com/problems/add-two-numbers/description/) | [Solution](https://github.com/twho/LeetCode-Swift/blob/master/Problems/1-100/Medium/0002-AddTwoNumbers.playground/Contents.swift) |
 | 0003 | 📙 | [Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [Solution](https://github.com/twho/LeetCode-Swift/blob/master/Problems/1-100/Medium/0003-LongestSubstringWithoutRepeatingCharacters.playground/Contents.swift) |
 | 0004 | 📕 | [Median of Two Sorted Arrays  ](https://leetcode.com/problems/median-of-two-sorted-arrays/) | [Solution](https://github.com/twho/LeetCode-Swift/blob/master/Problems/1-100/Hard/0004-MedianOfTwoSortedArrays.playground/Contents.swift) |
 | 0005 | 📙 | [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/) | [Solution](https://github.com/twho/LeetCode-Swift/blob/master/Problems/1-100/Medium/0005-LongestPalindromicSubstring.playground/Contents.swift) |
@@ -43,6 +43,7 @@ Straightforward solutions
 | 0028 | 📗 | [Implement strStr()](https://leetcode.com/problems/implement-strstr/description/) | [Solution](https://github.com/twho/LeetCode-Swift/blob/master/Problems/1-100/Easy/0028-ImplementstrStr().playground/Contents.swift)|
 | 0029 | 📙 | [Divide Two Integers](https://leetcode.com/problems/divide-two-integers/description/) | [Solution](https://github.com/twho/LeetCode-Swift/tree/master/Problems/1-100/Medium/0029-DivideTwoIntegers.playground/Contents.swift) |
 | 0033 | 📙 | [Search in Rotated Sorted Array](https://leetcode.com/problems/search-in-rotated-sorted-array/description/) | [Solution](https://github.com/twho/LeetCode-Swift/tree/master/Problems/1-100/Medium/0033-SearchInRotatedSortedArray.playground/Contents.swift)|
+| 0034 | 📙 | [Find First and Last Position of Element in Sorted Array](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/) | [Solution](https://github.com/twho/LeetCode-Swift/tree/master/Problems/1-100/Medium/0034-FindFirstandLastPositionElementSortedArray.playground/Contents.swift)|
 | 0035 | 📗 | [Search Insert Position](https://leetcode.com/problems/search-insert-position/) | [Solution](https://github.com/twho/LeetCode-Swift/blob/master/Problems/1-100/Easy/0035-SearchInsertPosition.playground/Contents.swift) |
 | 0039 | 📙 | [Combination Sum](https://leetcode.com/problems/combination-sum/) | [Solution](https://github.com/twho/LeetCode-Swift/tree/master/Problems/1-100/Medium/0039-CombinationSum.playground/Contents.swift) |
 |0040 | 📙 | [Combination Sum II](https://leetcode.com/problems/combination-sum-ii/) | [Solution](https://github.com/twho/LeetCode-Swift/tree/master/Problems/1-100/Medium/0040-CombinationSumII.playground/Contents.swift)|

Problems/101-200/Easy/0101-SymmetricTree.playground/Contents.swift

@@ -0,0 +1,99 @@
+// LeetCode: https://leetcode.com/problems/symmetric-tree/
+
+import XCTest
+
+public class TreeNode {
+    public var val: Int
+    public var left: TreeNode?
+    public var right: TreeNode?
+    public init(_ val: Int) {
+        self.val = val
+        self.left = nil
+        self.right = nil
+    }
+}
+
+class Solution {
+    func isSymmetric(_ root: TreeNode?) -> Bool {
+        var arr = [Int?]()
+        inOrder(root, &arr)
+        
+        if arr.count%2 == 0 {
+            return false
+        } else {
+            for i in 0..<arr.count/2 {
+                if arr[i] != arr[arr.count-1-i] {
+                    return false
+                }
+            }
+        }
+        return true
+    }
+    
+    private func inOrder(_ root: TreeNode?, _ arr: inout [Int?]) {
+        if root?.left == nil, root?.right == nil {
+            arr.append(root?.val)
+            return
+        }
+        inOrder(root?.left, &arr)
+        arr.append(root?.val)
+        inOrder(root?.right, &arr)
+    }
+}
+
+class Tests: XCTestCase {
+    let s = Solution()
+    
+    func testSample1() {
+        let input = buildTree([
+            1,
+            2, 2,
+            3, 4, 4, 3
+            ])
+        XCTAssertTrue(s.isSymmetric(input))
+    }
+    
+    func testSample2() {
+        let input = buildTree([
+            1,
+            2, 2,
+            2, nil, 2
+            ])
+        XCTAssertFalse(s.isSymmetric(input))
+    }
+    
+    func testSample3() {
+        let input = buildTree([
+            5,
+            4,1,
+            nil,1,nil,4,
+            2,nil,2,nil
+            ])
+        XCTAssertFalse(s.isSymmetric(input))
+    }
+    
+    private func buildTree(_ arr: [Int?]) -> TreeNode? {
+        guard arr.count > 0, let first = arr[0] else { return nil }
+        let root = TreeNode(first)
+        buildTree(0, root, arr)
+        return root
+    }
+    
+    private func buildTree(_ index: Int, _ root: TreeNode?, _ arr: [Int?]) {
+        guard let root = root else { return }
+        
+        if index < arr.count {
+            if 2*index+1 < arr.count, let val = arr[2*index+1] {
+                root.left = TreeNode(val)
+                buildTree(2*index+1, root.left, arr)
+            }
+            
+            if 2*index+2 < arr.count, let val = arr[2*index+2] {
+                root.right = TreeNode(val)
+                buildTree(2*index+2, root.right, arr)
+            }
+        }
+    }
+}
+
+Tests.defaultTestSuite.run()

Problems/101-200/Easy/0101-SymmetricTree.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>