add algorithm class LongetSubstring by GyooHa

Author: dawn-kgh

kotlin/src/main/kotlin/LongestSubstring.kt

@@ -0,0 +1,48 @@
+
+import kotlin.system.measureTimeMillis
+/*Example 1:
+Input: "abcabcbb"
+Output: 3
+Explanation: The answer is "abc", with the length of 3.
+Example 2:
+Input: "bbbbb"
+Output: 1
+Explanation: The answer is "b", with the length of 1.
+Example 3:
+Input: "pwwkew"
+Output: 3
+Explanation: The answer is "wke", with the length of 3.
+Note that the answer must be a substring, "pwke" is a subsequence and not a substring.*/
+class Solution2 {
+    fun lengthOfLongestSubstring(s: String): Int = if (s.length <= 1) s.length else recursive(s).length
+    private tailrec fun recursive(
+        s: String,
+        acc: String = ""
+    ): String = when {
+        s.isEmpty() -> acc
+        else -> {
+            val tail = s.drop(1)
+            val recursiveAcc = recursive2(s)
+            val greaterThan = acc.length > recursiveAcc.length
+            val result = if (greaterThan) acc else recursiveAcc
+            recursive(
+                tail,
+                result
+            )
+        }
+    }
+    private tailrec fun recursive2(
+        s: String,
+        acc: String = ""
+    ): String = when {
+        s.isEmpty() -> acc
+        else -> {
+            val head = s[0]
+            val tail = s.drop(1)
+            when {
+                acc.contains(head) -> acc
+                else -> recursive2(tail, acc + head)
+            }
+        }
+    }
+}