From 38a0bf2b12299a11ee422134d1e410d53d38a544 Mon Sep 17 00:00:00 2001
From: 0xff-dev <stevenshuang521@gmail.com>
Date: Thu, 4 Dec 2025 22:08:40 +0800
Subject: [PATCH] Add solution and test-cases for problem 2211

---
 .../2211.Count-Collisions-on-a-Road/README.md | 41 ++++++++++++-------
 .../Solution.go                               | 34 ++++++++++++++-
 .../Solution_test.go                          | 14 +++----
 3 files changed, 66 insertions(+), 23 deletions(-)

diff --git a/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/README.md b/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/README.md
index 2095a11f0..44be00920 100755
--- a/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/README.md
+++ b/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/README.md
@@ -1,28 +1,41 @@
 # [2211.Count Collisions on a Road][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
+There are `n` cars on an infinitely long road. The cars are numbered from `0` to `n - 1` from left to right and each car is present at a **unique** point.
+
+You are given a **0-indexed** string `directions` of length `n`. `directions[i]` can be either `'L'`, `'R'`, or `'S'` denoting whether the `ith` car is moving towards the **left**, towards the **right**, or **staying** at its current point respectively. Each moving car has the **same speed**.
+
+The number of collisions can be calculated as follows:
+
+- When two cars moving in **opposite** directions collide with each other, the number of collisions increases by `2`.
+- When a moving car collides with a stationary car, the number of collisions increases by `1`.
+
+After a collision, the cars involved can no longer move and will stay at the point where they collided. Other than that, cars cannot change their state or direction of motion.
+
+Return the **total number of collisions** that will happen on the road.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: directions = "RLRSLL"
+Output: 5
+Explanation:
+The collisions that will happen on the road are:
+- Cars 0 and 1 will collide with each other. Since they are moving in opposite directions, the number of collisions becomes 0 + 2 = 2.
+- Cars 2 and 3 will collide with each other. Since car 3 is stationary, the number of collisions becomes 2 + 1 = 3.
+- Cars 3 and 4 will collide with each other. Since car 3 is stationary, the number of collisions becomes 3 + 1 = 4.
+- Cars 4 and 5 will collide with each other. After car 4 collides with car 3, it will stay at the point of collision and get hit by car 5. The number of collisions becomes 4 + 1 = 5.
+Thus, the total number of collisions that will happen on the road is 5.
 ```
 
-## 题意
-> ...
-
-## 题解
+**Example 2:**
 
-### 思路1
-> ...
-Count Collisions on a Road
-```go
 ```
-
+Input: directions = "LLRR"
+Output: 0
+Explanation:
+No cars will collide with each other. Thus, the total number of collisions that will happen on the road is 0.
+```
 
 ## 结语
 
diff --git a/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/Solution.go b/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/Solution.go
index d115ccf5e..6ea23f9db 100644
--- a/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/Solution.go
+++ b/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/Solution.go
@@ -1,5 +1,35 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(directions string) int {
+	var ret int
+	l := len(directions)
+	points := [][2]int{}
+	for i := 0; i < l-1; i++ {
+		if directions[i] == 'R' && directions[i+1] == 'L' {
+			points = append(points, [2]int{i, i + 1})
+			continue
+		}
+		if directions[i] == 'S' {
+			points = append(points, [2]int{i, l})
+		}
+	}
+	if directions[l-1] == 'S' {
+		points = append(points, [2]int{l - 1, l})
+	}
+
+	for _, p := range points {
+		left := p[0] - 1
+		right := p[0] + 1
+		if p[1] != l {
+			ret += 2
+			right = p[1] + 1
+		}
+		for ; left >= 0 && directions[left] == 'R'; left-- {
+			ret++
+		}
+		for ; right < l && directions[right] == 'L'; right++ {
+			ret++
+		}
+	}
+	return ret
 }
diff --git a/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/Solution_test.go b/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/Solution_test.go
index 14ff50eb4..88a89e6dc 100644
--- a/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/Solution_test.go
+++ b/leetcode/2201-2300/2211.Count-Collisions-on-a-Road/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", "RLRSLL", 5},
+		{"TestCase2", "LLRR", 0},
+		{"TestCase3", "SRRLRLRSRLRSSRRLSLRLLRSLSLLSSRRLSRSLSLRRS", 28},
 	}
 
 	//	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() {
 }