Add solution and test-cases for problem 3623

Author: 0xff-dev

leetcode/3601-3700/3623.Count-Number-of-Trapezoids-I/1.png

@@ -1,28 +1,45 @@
 # [3623.Count Number of Trapezoids 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 2D integer array `points`, where `points[i] = [xi, yi]` represents the coordinates of the ith point on the Cartesian plane.
+
+A **horizontal trapezoid** is a convex quadrilateral with **at least one pair** of horizontal sides (i.e. parallel to the x-axis). Two lines are parallel if and only if they have the same slope.
+
+Return the number of unique **horizontal trapezoids** that can be formed by choosing any four distinct points from `points`.
 
-**Example 1:**
+Since the answer may be very large, return it **modulo** `10^9 + 7`.
+
+**Example 1:**  
+
+![1](./1.png)
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: points = [[1,0],[2,0],[3,0],[2,2],[3,2]]
+
+Output: 3
+
+Explanation:
+
+There are three distinct ways to pick four points that form a horizontal trapezoid:
+
+Using points [1,0], [2,0], [3,2], and [2,2].
+Using points [2,0], [3,0], [3,2], and [2,2].
+Using points [1,0], [3,0], [3,2], and [2,2].
 ```
 
-## 题意
-> ...
+**Example 2:**  
 
-## 题解
+![2](./2.png)
 
-### 思路1
-> ...
-Count Number of Trapezoids I
-```go
 ```
+Input: points = [[0,0],[1,0],[0,1],[2,1]]
 
+Output: 1
+
+Explanation:
+
+There is only one horizontal trapezoid that can be formed.
+```
 
 ## 结语
 

leetcode/3601-3700/3623.Count-Number-of-Trapezoids-I/2.png

@@ -1,5 +1,29 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+const mod = 1000000007
+
+func Solution(points [][]int) int {
+	columns := make(map[int]int)
+	for _, p := range points {
+		columns[p[1]]++
+	}
+
+	pairs := []int{}
+	sum, count := 0, 0
+	for _, c := range columns {
+		if c < 2 {
+			continue
+		}
+		count = c * (c - 1) / 2
+		sum = (sum + count) % mod
+		pairs = append(pairs, count)
+	}
+	var ret int
+	for _, pair := range pairs {
+		ret = (ret + pair*((sum-pair+mod)%mod)) % mod
+	}
+
+	// 使用模逆元乘以 1/2
+	inv2 := (mod + 1) / 2
+	return (ret * inv2) % mod
 }

leetcode/3601-3700/3623.Count-Number-of-Trapezoids-I/README.md

@@ -10,12 +10,11 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		inputs [][]int
+		expect int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", [][]int{{1, 0}, {2, 0}, {3, 0}, {2, 2}, {3, 2}}, 3},
+		{"TestCase2", [][]int{{0, 0}, {1, 0}, {0, 1}, {2, 1}}, 1},
 	}
 
 	//	开始测试
@@ -30,10 +29,10 @@ 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() {
 }