feat: Add solution for LeetCode problem 3

Author: WhiteHyun

longest-substring-without-repeating-characters/WhiteHyun.swift

@@ -0,0 +1,42 @@
+//  
+//  3. Longest Substring Without Repeating Characters
+//  https://leetcode.com/problems/longest-substring-without-repeating-characters/description/
+//  Dale-Study
+//  
+//  Created by WhiteHyun on 2024/06/08.
+//  
+
+class Solution {
+  func lengthOfLongestSubstring(_ s: String) -> Int {
+    var longest: Int = .min
+    let array = Array(s)
+
+    var set: Set<Character> = []
+    var temp: Int = 0
+    var startIndex = 0
+    for index in array.indices {
+      if set.contains(array[index]) == false {
+        set.insert(array[index])
+        temp += 1
+        continue
+      }
+
+      if longest < temp {
+        longest = temp
+      }
+
+      while array[startIndex] != array[index] {
+        set.remove(array[startIndex])
+        temp -= 1
+        startIndex += 1
+      }
+      startIndex += 1
+    }
+
+    if longest < temp {
+      longest = temp
+    }
+
+    return longest
+  }
+}