Add solution and test-cases for problem 3531

Author: 0xff-dev

leetcode/3501-3600/3531.Count-Covered-Buildings/1.jpg

@@ -1,28 +1,63 @@
 # [3531.Count Covered Buildings][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 positive integer `n`, representing an `n x n` city. You are also given a 2D grid `buildings`, where `buildings[i] = [x, y]` denotes a **unique** building located at coordinates `[x, y]`.
+
+A building is **covered** if there is at least one building in all **four** directions: left, right, above, and below.
+
+Return the number of **covered** buildings.
+
+**Example 1:**  
+
+![1](./1.jpg)
+
+```
+Input: n = 3, buildings = [[1,2],[2,2],[3,2],[2,1],[2,3]]
+
+Output: 1
+
+Explanation:
 
-**Example 1:**
+Only building [2,2] is covered as it has at least one building:
+above ([1,2])
+below ([3,2])
+left ([2,1])
+right ([2,3])
+Thus, the count of covered buildings is 1.
+```
+
+**Example 2:**  
+
+![2](./2.jpg)
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: n = 3, buildings = [[1,1],[1,2],[2,1],[2,2]]
+
+Output: 0
+
+Explanation:
+
+No building has at least one building in all four directions.
 ```
 
-## 题意
-> ...
+**Example 3:**  
 
-## 题解
+![3](./3.jpg)
 
-### 思路1
-> ...
-Count Covered Buildings
-```go
 ```
+Input: n = 5, buildings = [[1,3],[3,2],[3,3],[3,5],[5,3]]
+
+Output: 1
 
+Explanation:
+
+Only building [3,3] is covered as it has at least one building:
+above ([1,3])
+below ([5,3])
+left ([3,2])
+right ([3,5])
+Thus, the count of covered buildings is 1.
+```
 
 ## 结语
 

leetcode/3501-3600/3531.Count-Covered-Buildings/2.jpg

@@ -1,5 +1,45 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+import "sort"
+
+func Solution(n int, buildings [][]int) int {
+	var ret int
+	l := len(buildings)
+	byY := make([][]int, l)
+	byX := make([][]int, l)
+	copy(byY, buildings)
+	copy(byX, buildings)
+	sort.Slice(byY, func(i, j int) bool {
+		return byY[i][1] < byY[j][1]
+	})
+	sort.Slice(byX, func(i, j int) bool {
+		return byX[i][0] < byX[j][0]
+	})
+
+	yLoc := make(map[int][]int)
+	xLoc := make(map[int][]int)
+	for _, build := range byY {
+		xLoc[build[0]] = append(xLoc[build[0]], build[1])
+	}
+	for _, build := range byX {
+		yLoc[build[1]] = append(yLoc[build[1]], build[0])
+	}
+
+	for _, build := range buildings {
+		x, y := build[0], build[1]
+		index := sort.Search(len(xLoc[x]), func(i int) bool {
+			return xLoc[x][i] >= y
+		})
+		if index > 0 && index < len(xLoc[x])-1 {
+			j := sort.Search(len(yLoc[y]), func(ii int) bool {
+				return yLoc[y][ii] >= x
+			})
+			if j > 0 && j < len(yLoc[y])-1 {
+				ret++
+			}
+		}
+
+	}
+
+	return ret
 }

leetcode/3501-3600/3531.Count-Covered-Buildings/3.jpg

@@ -10,30 +10,31 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		n      int
+		inputs [][]int
+		expect int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", 3, [][]int{{1, 2}, {2, 2}, {3, 2}, {2, 1}, {2, 3}}, 1},
+		{"TestCase2", 3, [][]int{{1, 1}, {1, 2}, {2, 1}, {2, 2}}, 0},
+		{"TestCase3", 5, [][]int{{1, 3}, {3, 2}, {3, 3}, {3, 5}, {5, 3}}, 1},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
-			got := Solution(c.inputs)
+			got := Solution(c.n, c.inputs)
 			if !reflect.DeepEqual(got, c.expect) {
-				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
-					c.expect, got, c.inputs)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v",
+					c.expect, got, c.n, c.inputs)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }