2981. Find Longest Special Substring That Occurs Thrice I

Author: sergeyleschev

Diff for: 2501-3000/2981. Find Longest Special Substring That Occurs Thrice I.swift

@@ -0,0 +1,63 @@
+class Solution {
+
+    // Solution by Sergey Leschev
+    // 2981. Find Longest Special Substring That Occurs Thrice I
+
+    // Time complexity: O(N)
+    // Space complexity: O(N)
+
+    func maximumLength(_ s: String) -> Int {
+        var count = 0
+        var last = s[s.startIndex]
+        var ans = 0
+        var ump = [Character: [Int]]()
+
+        for c in s {
+            if c == last {
+                count += 1
+            } else {
+                if ump[last] == nil {
+                    ump[last] = [count]
+                } else {
+                    ump[last]?.append(count)
+                }
+                count = 1
+                last = c
+            }
+        }
+        if ump[last] == nil {
+            ump[last] = [count]
+        } else {
+            ump[last]?.append(count)
+        }
+
+        for (k, v) in ump {
+            var l1 = 0
+            var l2 = 0
+            var l3 = 0
+
+            for e in v {
+                if l1 < e {
+                    l3 = l2
+                    l2 = l1
+                    l1 = e
+                } else if l2 < e {
+                    l3 = l2
+                    l2 = e
+                } else if l3 < e {
+                    l3 = e
+                }
+            }
+
+            if l1 == l2 && l1 > l3 {
+                l2 -= 1
+            }
+
+            if l1 + l2 + l3 >= 3 {
+                ans = max(ans, l1 - 2, l2)
+            }
+        }
+
+        return ans != 0 ? ans : -1
+    }
+}