diff --git a/Algorithms/0815. Bus Routes/815. Bus Routes.go b/Algorithms/0815. Bus Routes/815. Bus Routes.go new file mode 100644 index 00000000..76f649ca --- /dev/null +++ b/Algorithms/0815. Bus Routes/815. Bus Routes.go @@ -0,0 +1,38 @@ +package leetcode + +func numBusesToDestination(routes [][]int, S int, T int) int { + if S == T { + return 0 + } + // vertexMap 中 key 是站点,value 是公交车数组,代表这些公交车路线可以到达此站点 + vertexMap, visited, queue, res := map[int][]int{}, make([]bool, len(routes)), []int{}, 0 + for i := 0; i < len(routes); i++ { + for _, v := range routes[i] { + tmp := vertexMap[v] + tmp = append(tmp, i) + vertexMap[v] = tmp + } + } + queue = append(queue, S) + for len(queue) > 0 { + res++ + qlen := len(queue) + for i := 0; i < qlen; i++ { + vertex := queue[0] + queue = queue[1:] + for _, bus := range vertexMap[vertex] { + if visited[bus] == true { + continue + } + visited[bus] = true + for _, v := range routes[bus] { + if v == T { + return res + } + queue = append(queue, v) + } + } + } + } + return -1 +} diff --git a/Algorithms/0815. Bus Routes/815. Bus Routes_test.go b/Algorithms/0815. Bus Routes/815. Bus Routes_test.go new file mode 100644 index 00000000..271d1370 --- /dev/null +++ b/Algorithms/0815. Bus Routes/815. Bus Routes_test.go @@ -0,0 +1,44 @@ +package leetcode + +import ( + "fmt" + "testing" +) + +type question815 struct { + para815 + ans815 +} + +// para 是参数 +// one 代表第一个参数 +type para815 struct { + r [][]int + s int + t int +} + +// ans 是答案 +// one 代表第一个答案 +type ans815 struct { + one int +} + +func Test_Problem815(t *testing.T) { + + qs := []question815{ + + question815{ + para815{[][]int{[]int{1, 2, 7}, []int{3, 6, 7}}, 1, 6}, + ans815{2}, + }, + } + + fmt.Printf("------------------------Leetcode Problem 815------------------------\n") + + for _, q := range qs { + _, p := q.ans815, q.para815 + fmt.Printf("【input】:%v 【output】:%v\n", p, numBusesToDestination(p.r, p.s, p.t)) + } + fmt.Printf("\n\n\n") +} diff --git a/Algorithms/0815. Bus Routes/README.md b/Algorithms/0815. Bus Routes/README.md new file mode 100755 index 00000000..59c8b1b9 --- /dev/null +++ b/Algorithms/0815. Bus Routes/README.md @@ -0,0 +1,41 @@ +# [815. Bus Routes](https://leetcode.com/problems/bus-routes/) + + +## 题目: + +We have a list of bus routes. Each `routes[i]` is a bus route that the i-th bus repeats forever. For example if `routes[0] = [1, 5, 7]`, this means that the first bus (0-th indexed) travels in the sequence 1->5->7->1->5->7->1->... forever. + +We start at bus stop `S` (initially not on a bus), and we want to go to bus stop `T`. Travelling by buses only, what is the least number of buses we must take to reach our destination? Return -1 if it is not possible. + + Example: + Input: + routes = [[1, 2, 7], [3, 6, 7]] + S = 1 + T = 6 + Output: 2 + Explanation: + The best strategy is take the first bus to the bus stop 7, then take the second bus to the bus stop 6. + +**Note:** + +- `1 <= routes.length <= 500`. +- `1 <= routes[i].length <= 500`. +- `0 <= routes[i][j] < 10 ^ 6`. + + +## 题目大意 + +我们有一系列公交路线。每一条路线 routes[i] 上都有一辆公交车在上面循环行驶。例如,有一条路线 routes[0] = [1, 5, 7],表示第一辆 (下标为0) 公交车会一直按照 1->5->7->1->5->7->1->... 的车站路线行驶。假设我们从 S 车站开始(初始时不在公交车上),要去往 T 站。 期间仅可乘坐公交车,求出最少乘坐的公交车数量。返回 -1 表示不可能到达终点车站。 + + +说明: + +- 1 <= routes.length <= 500. +- 1 <= routes[i].length <= 500. +- 0 <= routes[i][j] < 10 ^ 6. + + +## 解题思路 + +- 给出一些公交路线,公交路径代表经过的哪些站。现在给出起点和终点站,问最少需要换多少辆公交车才能从起点到终点? +- 这一题可以转换成图论的问题,将每个站台看成顶点,公交路径看成每个顶点的边。同一个公交的边染色相同。题目即可转化为从顶点 S 到顶点 T 需要经过最少多少条不同的染色边。用 BFS 即可轻松解决。从起点 S 开始,不断的扩展它能到达的站点。用 visited 数组防止放入已经可达的站点引起的环。用 map 存储站点和公交车的映射关系(即某个站点可以由哪些公交车到达),BFS 的过程中可以用这个映射关系,拿到公交车的其他站点信息,从而扩张队列里面的可达站点。一旦扩展出现了终点 T,就可以返回结果了。 diff --git a/README.md b/README.md index b5156170..19577392 100644 --- a/README.md +++ b/README.md @@ -879,7 +879,7 @@ | 0812 | Largest Triangle Area | | 56.30% | Easy | | | 0813 | Largest Sum of Averages | | 45.50% | Medium | | | 0814 | Binary Tree Pruning | | 71.20% | Medium | | -| 0815 | Bus Routes | | 40.30% | Hard | | +| 0815 | Bus Routes | [Go](https://github.com/halfrost/LeetCode-Go/tree/master/Algorithms/0815.%20Bus%20Routes) | 40.30% | Hard | | | 0816 | Ambiguous Coordinates | | 44.20% | Medium | | | 0817 | Linked List Components | [Go](https://github.com/halfrost/LeetCode-Go/tree/master/Algorithms/0817.%20Linked%20List%20Components) | 54.80% | Medium | | | 0818 | Race Car | | 35.20% | Hard | |