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‎Problemset/0815-Bus Routes/README.md

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# 815. Bus Routes
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You are given an array `routes` representing bus routes where `routes[i]` is a bus route that the <code>i<sup>th</sup></code> bus repeats forever.
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* For example, if `routes[0] = [1, 5, 7]`, this means that the <code>0<sup>th</sup></code> bus travels in the sequence `1 -> 5 -> 7 -> 1 -> 5 -> 7 -> 1 -> ...` forever.
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You will start at the bus stop `source` (You are not on any bus initially), and you want to go to the bus stop `target`. You can travel between bus stops by buses only.
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Return *the least number of buses you must take to travel from* `source` *to* `target`. Return `-1` if it is not possible.
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#### Example 1:
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<pre>
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<strong>Input:</strong> routes = [[1,2,7],[3,6,7]], source = 1, target = 6
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> The best strategy is take the first bus to the bus stop 7, then take the second bus to the bus stop 6.
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</pre>
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#### Example 2:
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<pre>
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<strong>Input:</strong> routes = [[7,12],[4,5,15],[6],[15,19],[9,12,13]], source = 15, target = 12
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<strong>Output:</strong> -1
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</pre>
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#### Constraints:
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* `1 <= routes.length <= 500`.
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* <code>1 <= routes[i].length <= 10<sup>5</sup></code>
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* All the values of `routes[i]` are **unique**.
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* <code>sum(routes[i].length) <= 10<sup>5</sup></code>
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* <code>0 <= routes[i][j] < 10<sup>6</sup></code>
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* <code>0 <= source, target < 10<sup>6</sup></code>
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## Solutions (Rust)
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### 1. Solution
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```Rust
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use std::collections::HashMap;
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use std::collections::HashSet;
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use std::collections::VecDeque;
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impl Solution {
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pub fn num_buses_to_destination(routes: Vec<Vec<i32>>, source: i32, target: i32) -> i32 {
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if source == target {
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return 0;
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}
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let mut routes = routes
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.into_iter()
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.map(|route| route.into_iter().collect::<HashSet<_>>())
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.collect::<Vec<_>>();
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let mut deque = VecDeque::new();
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let mut visited = HashSet::new();
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let mut neighbors = vec![vec![]; routes.len()];
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for i in 0..routes.len() {
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if routes[i].contains(&source) {
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deque.push_back((i, 1));
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visited.insert(i);
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}
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for j in i + 1..routes.len() {
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for stop in routes[i].iter() {
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if routes[j].contains(stop) {
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neighbors[i].push(j);
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neighbors[j].push(i);
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break;
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}
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}
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}
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}
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while let Some((i, buses)) = deque.pop_front() {
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if routes[i].contains(&target) {
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return buses;
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}
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for &j in &neighbors[i] {
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if !visited.contains(&j) {
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deque.push_back((j, buses + 1));
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visited.insert(j);
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}
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}
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}
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-1
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}
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}
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```

‎Problemset/0815-Bus Routes/README_CN.md

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# 815. 公交路线
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给你一个数组 `routes` ，表示一系列公交线路，其中每个 `routes[i]` 表示一条公交线路，第 `i` 辆公交车将会在上面循环行驶。
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* 例如，路线 `routes[0] = [1, 5, 7]` 表示第 `0` 辆公交车会一直按序列 `1 -> 5 -> 7 -> 1 -> 5 -> 7 -> 1 -> ...` 这样的车站路线行驶。
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现在从 `source` 车站出发（初始时不在公交车上），要前往 `target` 车站。 期间仅可乘坐公交车。
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求出 **最少乘坐的公交车数量** 。如果不可能到达终点车站，返回 `-1` 。
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#### 示例 1:
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<pre>
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<strong>输入:</strong> routes = [[1,2,7],[3,6,7]], source = 1, target = 6
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<strong>输出:</strong> 2
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<strong>解释:</strong> 最优策略是先乘坐第一辆公交车到达车站 7 , 然后换乘第二辆公交车到车站 6 。
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</pre>
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#### 示例 2:
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<pre>
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<strong>输入:</strong> routes = [[7,12],[4,5,15],[6],[15,19],[9,12,13]], source = 15, target = 12
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<strong>输出:</strong> -1
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</pre>
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#### 提示:
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* `1 <= routes.length <= 500`.
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* <code>1 <= routes[i].length <= 10<sup>5</sup></code>
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* `routes[i]` 中的所有值 **互不相同**
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* <code>sum(routes[i].length) <= 10<sup>5</sup></code>
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* <code>0 <= routes[i][j] < 10<sup>6</sup></code>
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* <code>0 <= source, target < 10<sup>6</sup></code>
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## 题解 (Rust)
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### 1. 题解
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```Rust
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use std::collections::HashMap;
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use std::collections::HashSet;
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use std::collections::VecDeque;
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impl Solution {
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pub fn num_buses_to_destination(routes: Vec<Vec<i32>>, source: i32, target: i32) -> i32 {
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if source == target {
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return 0;
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}
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let mut routes = routes
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.into_iter()
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.map(|route| route.into_iter().collect::<HashSet<_>>())
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.collect::<Vec<_>>();
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let mut deque = VecDeque::new();
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let mut visited = HashSet::new();
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let mut neighbors = vec![vec![]; routes.len()];
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for i in 0..routes.len() {
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if routes[i].contains(&source) {
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deque.push_back((i, 1));
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visited.insert(i);
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}
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for j in i + 1..routes.len() {
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for stop in routes[i].iter() {
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if routes[j].contains(stop) {
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neighbors[i].push(j);
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neighbors[j].push(i);
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break;
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}
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}
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}
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}
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while let Some((i, buses)) = deque.pop_front() {
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if routes[i].contains(&target) {
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return buses;
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}
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for &j in &neighbors[i] {
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if !visited.contains(&j) {
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deque.push_back((j, buses + 1));
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visited.insert(j);
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}
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}
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}
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-1
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}
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}
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```

‎Problemset/0815-Bus Routes/Solution.rs

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use std::collections::HashMap;
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use std::collections::HashSet;
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use std::collections::VecDeque;
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impl Solution {
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pub fn num_buses_to_destination(routes: Vec<Vec<i32>>, source: i32, target: i32) -> i32 {
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if source == target {
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return 0;
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}
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let mut routes = routes
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.into_iter()
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.map(|route| route.into_iter().collect::<HashSet<_>>())
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.collect::<Vec<_>>();
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let mut deque = VecDeque::new();
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let mut visited = HashSet::new();
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let mut neighbors = vec![vec![]; routes.len()];
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for i in 0..routes.len() {
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if routes[i].contains(&source) {
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deque.push_back((i, 1));
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visited.insert(i);
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}
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for j in i + 1..routes.len() {
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for stop in routes[i].iter() {
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if routes[j].contains(stop) {
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neighbors[i].push(j);
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neighbors[j].push(i);
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break;
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}
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}
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}
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}
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while let Some((i, buses)) = deque.pop_front() {
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if routes[i].contains(&target) {
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return buses;
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}
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for &j in &neighbors[i] {
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if !visited.contains(&j) {
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deque.push_back((j, buses + 1));
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visited.insert(j);
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}
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}
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}
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-1
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}
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}

‎README.md

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[812][812l] |[Largest Triangle Area][812] |![rs]
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[813][813l] |[Largest Sum of Averages][813] |![py]
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[814][814l] |[Binary Tree Pruning][814] |![py]&nbsp;&nbsp;![rb]
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[815][815l] |[Bus Routes][815] |![rs]
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[816][816l] |[Ambiguous Coordinates][816] |![rs]
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[817][817l] |[Linked List Components][817] |![py]&nbsp;&nbsp;![rb]
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[819][819l] |[Most Common Word][819] |![py]
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[812]:Problemset/0812-Largest%20Triangle%20Area/README.md#812-largest-triangle-area
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[813]:Problemset/0813-Largest%20Sum%20of%20Averages/README.md#813-largest-sum-of-averages
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[814]:Problemset/0814-Binary%20Tree%20Pruning/README.md#814-binary-tree-pruning
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[815]:Problemset/0815-Bus%20Routes/README.md#815-bus-routes
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[816]:Problemset/0816-Ambiguous%20Coordinates/README.md#816-ambiguous-coordinates
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[817]:Problemset/0817-Linked%20List%20Components/README.md#817-linked-list-components
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[819]:Problemset/0819-Most%20Common%20Word/README.md#819-most-common-word
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[812l]:https://leetcode.com/problems/largest-triangle-area/
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[813l]:https://leetcode.com/problems/largest-sum-of-averages/
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[814l]:https://leetcode.com/problems/binary-tree-pruning/
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[815l]:https://leetcode.com/problems/bus-routes/
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[816l]:https://leetcode.com/problems/ambiguous-coordinates/
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[817l]:https://leetcode.com/problems/linked-list-components/
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[819l]:https://leetcode.com/problems/most-common-word/

‎README_CN.md

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[812][812l] |[最大三角形面积][812] |![rs]
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[813][813l] |[最大平均值和的分组][813] |![py]
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[814][814l] |[二叉树剪枝][814] |![py]&nbsp;&nbsp;![rb]
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[815][815l] |[公交路线][815] |![rs]
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[816][816l] |[模糊坐标][816] |![rs]
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[817][817l] |[链表组件][817] |![py]&nbsp;&nbsp;![rb]
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[819][819l] |[最常见的单词][819] |![py]
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[812]:Problemset/0812-Largest%20Triangle%20Area/README_CN.md#812-最大三角形面积
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[813]:Problemset/0813-Largest%20Sum%20of%20Averages/README_CN.md#813-最大平均值和的分组
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[814]:Problemset/0814-Binary%20Tree%20Pruning/README_CN.md#814-二叉树剪枝
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[815]:Problemset/0815-Bus%20Routes/README_CN.md#815-公交路线
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[816]:Problemset/0816-Ambiguous%20Coordinates/README_CN.md#816-模糊坐标
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[817]:Problemset/0817-Linked%20List%20Components/README_CN.md#817-链表组件
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[819]:Problemset/0819-Most%20Common%20Word/README_CN.md#819-最常见的单词
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[812l]:https://leetcode.cn/problems/largest-triangle-area/
37793781
[813l]:https://leetcode.cn/problems/largest-sum-of-averages/
37803782
[814l]:https://leetcode.cn/problems/binary-tree-pruning/
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[815l]:https://leetcode.cn/problems/bus-routes/
37813784
[816l]:https://leetcode.cn/problems/ambiguous-coordinates/
37823785
[817l]:https://leetcode.cn/problems/linked-list-components/
37833786
[819l]:https://leetcode.cn/problems/most-common-word/

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