From f780e59e039198eabb44463ea35970240b63d40e Mon Sep 17 00:00:00 2001
From: 0xff-dev <stevenshuang521@gmail.com>
Date: Tue, 10 Dec 2024 09:31:14 +0800
Subject: [PATCH] Add solution and test-cases for problem 2981

---
 .../README.md                                 | 37 ++++++++++++-------
 .../Solution.go                               | 37 ++++++++++++++++++-
 .../Solution_test.go                          | 14 +++----
 3 files changed, 66 insertions(+), 22 deletions(-)

diff --git a/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/README.md b/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/README.md
index dea27366..a96dc9f0 100755
--- a/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/README.md
+++ b/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/README.md
@@ -1,28 +1,39 @@
 # [2981.Find Longest Special Substring That Occurs Thrice I][title]
 
-> [!WARNING|style:flat]
-> This question is temporarily unanswered if you have good ideas. Welcome to [Create Pull Request PR](https://github.com/kylesliu/awesome-golang-algorithm)
-
 ## Description
+You are given a string `s` that consists of lowercase English letters.
+
+A string is called **special** if it is made up of only a single character. For example, the string `"abc"` is not special, whereas the strings `"ddd"`, `"zz"`, and `"f"` are special.
+
+Return the length of the **longest special substring** of `s` which occurs **at least thrice**, or `-1` if no special substring occurs at least thrice.
+
+A **substring** is a contiguous **non-empty** sequence of characters within a string.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: s = "aaaa"
+Output: 2
+Explanation: The longest special substring which occurs thrice is "aa": substrings "aaaa", "aaaa", and "aaaa".
+It can be shown that the maximum length achievable is 2.
 ```
 
-## 题意
-> ...
-
-## 题解
+**Example 2:**
 
-### 思路1
-> ...
-Find Longest Special Substring That Occurs Thrice I
-```go
 ```
+Input: s = "abcdef"
+Output: -1
+Explanation: There exists no special substring which occurs at least thrice. Hence return -1.
+```
+
+**Example 3:**
 
+```
+Input: s = "abcaba"
+Output: 1
+Explanation: The longest special substring which occurs thrice is "a": substrings "abcaba", "abcaba", and "abcaba".
+It can be shown that the maximum length achievable is 1.
+```
 
 ## 结语
 
diff --git a/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/Solution.go b/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/Solution.go
index d115ccf5..a65264e6 100644
--- a/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/Solution.go
+++ b/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/Solution.go
@@ -1,5 +1,38 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(s string) int {
+	ans := -1
+	cache := [26]map[int]int{}
+	for i := range 26 {
+		cache[i] = make(map[int]int)
+	}
+	l := len(s)
+	start := 0
+	cur := s[start]
+	for i := 1; i < l; i++ {
+		if s[i] == cur {
+			continue
+		}
+
+		index := cur - 'a'
+		count := i - start
+		for ll := 1; ll <= count; ll++ {
+			cache[index][ll] += count - ll + 1
+			if cache[index][ll] >= 3 && ll > ans {
+				ans = ll
+			}
+		}
+		cur = s[i]
+		start = i
+	}
+	index := cur - 'a'
+	count := l - start
+	for ll := 1; ll <= count; ll++ {
+		cache[index][ll] += count - ll + 1
+		if cache[index][ll] >= 3 && ll > ans {
+			ans = ll
+		}
+	}
+
+	return ans
 }
diff --git a/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/Solution_test.go b/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/Solution_test.go
index 14ff50eb..5a0ff5a4 100644
--- a/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/Solution_test.go
+++ b/leetcode/2901-3000/2981.Find-Longest-Special-Substring-That-Occurs-Thrice-I/Solution_test.go
@@ -10,12 +10,12 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		inputs string
+		expect int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", "aaaa", 2},
+		{"TestCase2", "abcdef", -1},
+		{"TestCase3", "abcaba", 1},
 	}
 
 	//	开始测试
@@ -30,10 +30,10 @@ func TestSolution(t *testing.T) {
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }