Add solution and test-cases for problem 417

leetcode/401-500/0417.Pacific-Atlantic-Water-Flow/README.md

@@ -1,28 +1,46 @@
 # [417.Pacific Atlantic Water Flow][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 is an `m x n` rectangular island that borders both the **Pacific Ocean** and **Atlantic Ocean**. The **Pacific Ocean** touches the island's left and top edges, and the **Atlantic Ocean** touches the island's right and bottom edges.
 
-**Example 1:**
+The island is partitioned into a grid of square cells. You are given an `m x n` integer matrix `heights` where `heights[r][c]` represents the **height above sea level** of the cell at coordinate `(r, c)`.
 
-```
-Input: a = "11", b = "1"
-Output: "100"
-```
+The island receives a lot of rain, and the rain water can flow to neighboring cells directly north, south, east, and west if the neighboring cell's height is **less than or equal to** the current cell's height. Water can flow from any cell adjacent to an ocean into the ocean.
+
+Return a **2D list** of grid coordinates `result` where `result[i] = [ri, ci]` denotes that rain water can flow from cell `(ri, ci)` to **both** the Pacific and Atlantic oceans.
 
-## 题意
-> ...
+**Example 1:**  
 
-## 题解
+![1](./1.jpg)
 
-### 思路1
-> ...
-Pacific Atlantic Water Flow
-```go
 ```
+Input: heights = [[1,2,2,3,5],[3,2,3,4,4],[2,4,5,3,1],[6,7,1,4,5],[5,1,1,2,4]]
+Output: [[0,4],[1,3],[1,4],[2,2],[3,0],[3,1],[4,0]]
+Explanation: The following cells can flow to the Pacific and Atlantic oceans, as shown below:
+[0,4]: [0,4] -> Pacific Ocean 
+       [0,4] -> Atlantic Ocean
+[1,3]: [1,3] -> [0,3] -> Pacific Ocean 
+       [1,3] -> [1,4] -> Atlantic Ocean
+[1,4]: [1,4] -> [1,3] -> [0,3] -> Pacific Ocean 
+       [1,4] -> Atlantic Ocean
+[2,2]: [2,2] -> [1,2] -> [0,2] -> Pacific Ocean 
+       [2,2] -> [2,3] -> [2,4] -> Atlantic Ocean
+[3,0]: [3,0] -> Pacific Ocean 
+       [3,0] -> [4,0] -> Atlantic Ocean
+[3,1]: [3,1] -> [3,0] -> Pacific Ocean 
+       [3,1] -> [4,1] -> Atlantic Ocean
+[4,0]: [4,0] -> Pacific Ocean 
+       [4,0] -> Atlantic Ocean
+Note that there are other possible paths for these cells to flow to the Pacific and Atlantic oceans.
+```
+
+**Example 2:**
 
+```
+Input: heights = [[1]]
+Output: [[0,0]]
+Explanation: The water can flow from the only cell to the Pacific and Atlantic oceans.
+```
 
 ## 结语
 

leetcode/401-500/0417.Pacific-Atlantic-Water-Flow/Solution.go

@@ -1,5 +1,76 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(heights [][]int) [][]int {
+	m, n := len(heights), len(heights[0])
+	state := make([][]int, m)
+	pacific, atlantic := 1, 2
+	for i := 0; i < m; i++ {
+		state[i] = make([]int, n)
+	}
+	for i := 0; i < n-1; i++ {
+		state[0][i] = pacific
+		state[m-1][i+1] = atlantic
+	}
+	for i := 0; i < m-1; i++ {
+		state[i][0] = pacific
+		state[i+1][n-1] = atlantic
+	}
+
+	state[0][n-1] = 3
+	state[m-1][0] = 3
+	var (
+		leftTop     func(int, int, int)
+		rightBottom func(int, int, int)
+	)
+	leftTop = func(x, y, pre int) {
+		if x < 0 || x >= m || y < 0 || y >= n {
+			return
+		}
+		if pre != -1 && state[x][y]&pacific == pacific {
+			return
+		}
+		if heights[x][y] < pre {
+			return
+		}
+		state[x][y] |= pacific
+		leftTop(x-1, y, heights[x][y])
+		leftTop(x+1, y, heights[x][y])
+		leftTop(x, y+1, heights[x][y])
+		leftTop(x, y-1, heights[x][y])
+	}
+	rightBottom = func(x, y, pre int) {
+		if x < 0 || x >= m || y < 0 || y >= n {
+			return
+		}
+		if heights[x][y] < pre {
+			return
+		}
+		if pre != -1 && state[x][y]&atlantic == atlantic {
+			return
+		}
+		state[x][y] |= atlantic
+		rightBottom(x-1, y, heights[x][y])
+		rightBottom(x+1, y, heights[x][y])
+		rightBottom(x, y-1, heights[x][y])
+		rightBottom(x, y+1, heights[x][y])
+	}
+
+	for i := 0; i < n; i++ {
+		leftTop(0, i, -1)
+		rightBottom(m-1, i, -1)
+	}
+	for i := 0; i < m; i++ {
+		leftTop(i, 0, -1)
+		rightBottom(i, n-1, -1)
+	}
+	res := make([][]int, 0)
+	for i := 0; i < m; i++ {
+		for j := 0; j < n; j++ {
+			if state[i][j] == 3 {
+				res = append(res, []int{i, j})
+			}
+		}
+	}
+
+	return res
 }

leetcode/401-500/0417.Pacific-Atlantic-Water-Flow/Solution_test.go

@@ -10,12 +10,15 @@ 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, 2, 2, 3, 5}, {3, 2, 3, 4, 4}, {2, 4, 5, 3, 1}, {6, 7, 1, 4, 5}, {5, 1, 1, 2, 4},
+		}, [][]int{
+			{0, 4}, {1, 3}, {1, 4}, {2, 2}, {3, 0}, {3, 1}, {4, 0},
+		}},
+		{"TestCase2", [][]int{{1}}, [][]int{{0, 0}}},
 	}
 
 	//	开始测试
@@ -30,10 +33,10 @@ 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() {
 }