[Hyun] Week 1 Solutions

best-time-to-buy-and-sell-stock/WhiteHyun.swift

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+//
+//  121. Best Time to Buy and Sell Stock.swift
+//  https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/
+//  Algorithm
+//
+//  Created by 홍승현 on 2024/04/26.
+//
+
+import Foundation
+
+final class LeetCode121 {
+  func maxProfit(_ prices: [Int]) -> Int {
+    if prices.count == 1 { return 0 }
+    var diff = 0
+    var left = 0
+    var right = 0
+
+    while right < prices.endIndex {
+      if prices[left] > prices[right] {
+        left = right
+      } else {
+        diff = max(diff, prices[right] - prices[left])
+      }
+      right += 1
+    }
+    return diff
+  }
+}

contains-duplicate/WhiteHyun.swift

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+//
+//  217. Contains Duplicate.swift
+//  https://leetcode.com/problems/contains-duplicate/description/
+//  Algorithm
+//
+//  Created by 홍승현 on 2024/04/26.
+//
+
+import Foundation
+
+final class LeetCode217 {
+  func containsDuplicate(_ nums: [Int]) -> Bool {
+    Set(nums).count != nums.count
+  }
+}

two-sum/WhiteHyun.swift

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+//
+//  1. Two Sum.swift
+//  https://leetcode.com/problems/two-sum/description/
+//  Algorithm
+//
+//  Created by 홍승현 on 2024/04/26.
+//
+
+import Foundation
+
+final class LeetCode1 {
+  func twoSum(_ numbers: [Int], _ target: Int) -> [Int] {
+    let sortedNumbersWithIndex = numbers.enumerated().sorted { lhs, rhs in
+      lhs.element < rhs.element
+    }
+    var left = 0
+    var right = sortedNumbersWithIndex.endIndex - 1
+
+    while left < right {
+      let sum = sortedNumbersWithIndex[left].element + sortedNumbersWithIndex[right].element
+      if sum == target { break }
+      if sum < target {
+        left += 1
+      } else {
+        right -= 1
+      }
+    }
+
+    return [sortedNumbersWithIndex[left].offset, sortedNumbersWithIndex[right].offset]
+  }
+}

valid-anagram/WhiteHyun.swift

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+//
+//  242. Valid Anagram.swift
+//  https://leetcode.com/problems/valid-anagram/description/
+//  Algorithm
+//
+//  Created by 홍승현 on 2024/04/26.
+//
+
+import Foundation
+
+final class LeetCode242 {
+  func isAnagram(_ s: String, _ t: String) -> Bool {
+    Dictionary(s.map { ($0, 1) }, uniquingKeysWith: +) == Dictionary(t.map { ($0, 1) }, uniquingKeysWith: +)
+  }
+}

valid-palindrome/WhiteHyun.swift

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+//
+//  125. Valid Palindrome.swift
+//  https://leetcode.com/problems/valid-palindrome/description/
+//  Algorithm
+//
+//  Created by 홍승현 on 2024/04/26.
+//
+
+import Foundation
+
+final class LeetCode125 {
+  func isPalindrome(_ s: String) -> Bool {
+    if let regex = try? NSRegularExpression(pattern: "[a-zA-Z0-9]+") {
+      let string = regex
+        .matches(in: s, range: .init(location: 0, length: s.count))
+        .map { s[Range($0.range, in: s)!].lowercased() }
+        .joined()
+
+      return string == String(string.reversed())
+    }
+
+    return false
+  }
+
+  func isPalindromeUsingRegexString(_ s: String) -> Bool {
+    var alphabets = ""
+    for match in s.matches(of: /(?<alphabet>[a-zA-Z0-9]+)/) {
+      alphabets += match.alphabet.lowercased()
+    }
+    return String(alphabets.reversed()) == alphabets
+  }
+}