2982. Find Longest Special Substring That Occurs Thrice II

Author: sergeyleschev

2501-3000/2982. Find Longest Special Substring That Occurs Thrice II.swift

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+class Solution {
+
+    // Solution by Sergey Leschev
+    // 2982. Find Longest Special Substring That Occurs Thrice II
+
+    // Time complexity: O(N)
+    // Space complexity: O(1)
+
+    func maximumLength(_ s: String) -> Int {
+        var count = 0
+        var last = s.first!
+        var ans = 0
+        var ump = [Character: [Int]]()
+
+        for char in s {
+            if char == last {
+                count += 1
+            } else {
+                ump[last, default: []].append(count)
+
+                if ump[last]!.count >= 4 {
+                    ump[last]?.sort(by: >)
+                    ump[last]?.removeLast()
+                }
+
+                count = 1
+                last = char
+            }
+        }
+
+        ump[last, default: []].append(count)
+
+        for (_, v) in ump {
+            var l1 = 0
+            var l2 = 0
+            var l3 = 0
+
+            for e in v {
+                if l1 < e {
+                    (l3, l2, l1) = (l2, 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
+    }
+}