Merge pull request #899 from 0xff-dev/778

Add solution and test-cases for problem 778

Author: 6boris

leetcode/701-800/0778.Swim-in-Rising-Water/README.md

@@ -1,28 +1,36 @@
 # [778.Swim in Rising Water][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 an `n x n` integer matrix `grid` where each value `grid[i][j]` represents the elevation at that point `(i, j)`.
+
+The rain starts to fall. At time `t`, the depth of the water everywhere is `t`. You can swim from a square to another 4-directionally adjacent square if and only if the elevation of both squares individually are at most `t`. You can swim infinite distances in zero time. Of course, you must stay within the boundaries of the grid during your swim.
+
+Return the least time until you can reach the bottom right square `(n - 1, n - 1)` if you start at the top left square `(0, 0)`.
 
-**Example 1:**
+**Example 1:**  
+
+![1](./swim1-grid.jpeg)
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: grid = [[0,2],[1,3]]
+Output: 3
+Explanation:
+At time 0, you are in grid location (0, 0).
+You cannot go anywhere else because 4-directionally adjacent neighbors have a higher elevation than t = 0.
+You cannot reach point (1, 1) until time 3.
+When the depth of water is 3, we can swim anywhere inside the grid.
 ```
 
-## 题意
-> ...
+**Example 2:**  
 
-## 题解
+![2](./swim2-grid-1.jpeg)
 
-### 思路1
-> ...
-Swim in Rising Water
-```go
 ```
-
+Input: grid = [[0,1,2,3,4],[24,23,22,21,5],[12,13,14,15,16],[11,17,18,19,20],[10,9,8,7,6]]
+Output: 16
+Explanation: The final route is shown.
+We need to wait until time 16 so that (0, 0) and (4, 4) are connected.
+```
 
 ## 结语
 

leetcode/701-800/0778.Swim-in-Rising-Water/Solution.go

@@ -1,5 +1,44 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func dfs778(grid [][]int, visited [][]bool, x, y, t int) bool {
+	if x < 0 || x >= len(grid) || y < 0 || y >= len(grid) || visited[x][y] || grid[x][y] > t {
+		return false
+	}
+	if x == len(grid)-1 && y == len(grid)-1 {
+		return true
+	}
+	visited[x][y] = true
+	return dfs778(grid, visited, x-1, y, t) ||
+		dfs778(grid, visited, x+1, y, t) ||
+		dfs778(grid, visited, x, y-1, t) ||
+		dfs778(grid, visited, x, y+1, t)
+
+}
+func do778(grid [][]int, x, y, t int) bool {
+	gridCopy := make([][]int, len(grid))
+	v := make([][]bool, len(grid))
+	for i := 0; i < len(grid); i++ {
+		gridCopy[i] = make([]int, len(grid))
+		v[i] = make([]bool, len(grid))
+		copy(gridCopy[i], grid[i])
+	}
+
+	return dfs778(gridCopy, v, x, y, t)
+}
+func Solution(grid [][]int) int {
+
+	// 一般这种dfs或者bfs都不太好确定的题，可以尝试binary search+dfs
+	// 直接尝试搜索每个答案
+	ans := -1
+	l, r := 0, 1<<31-1
+	for l <= r {
+		mid := l + (r-l)/2
+		if do778(grid, 0, 0, mid) {
+			ans = mid
+			r = mid - 1
+		} else {
+			l = mid + 1
+		}
+	}
+	return ans
 }

leetcode/701-800/0778.Swim-in-Rising-Water/Solution_test.go

@@ -10,12 +10,19 @@ 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{
+			{0, 2}, {1, 3},
+		}, 3},
+		{"TestCase1", [][]int{
+			{0, 1, 2, 3, 4},
+			{24, 23, 22, 21, 5},
+			{12, 13, 14, 15, 16},
+			{11, 17, 18, 19, 20},
+			{10, 9, 8, 7, 6},
+		}, 16},
 	}
 
 	//	开始测试
@@ -30,10 +37,10 @@ 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() {
 }