为有牺牲多壮志，敢教日月换新天。

[Swift]LeetCode743. 网络延迟时间 | Network Delay Time

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公众号：山青咏芝（shanqingyongzhi）
➤博客园地址：山青咏芝（https://www.cnblogs.com/strengthen/）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址： https://www.cnblogs.com/strengthen/p/10525029.html 
➤如果链接不是山青咏芝的博客园地址，则可能是爬取作者的文章。
➤原文已修改更新！强烈建议点击原文地址阅读！支持作者！支持原创！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

热烈欢迎，请直接点击！！！

进入博主App Store主页，下载使用各个作品！！！

注：博主将坚持每月上线一个新app！！！

There are N network nodes, labelled 1 to N.

Given times, a list of travel times as directededges times[i] = (u, v, w), where u is the source node, v is the target node, and w is the time it takes for a signal to travel from source to target.

Now, we send a signal from a certain node K. How long will it take for all nodes to receive the signal? If it is impossible, return -1.

Note:

  1. N will be in the range [1, 100].
  2. K will be in the range [1, N].
  3. The length of times will be in the range [1, 6000].
  4. All edges times[i] = (u, v, w) will have 1 <= u, v <= N and 0 <= w <= 100.

有 N 个网络节点，标记为 1 到 N。

给定一个列表 times，表示信号经过有向边的传递时间。 times[i] = (u, v, w)，其中 u 是源节点，v 是目标节点， w 是一个信号从源节点传递到目标节点的时间。

现在，我们向当前的节点 K 发送了一个信号。需要多久才能使所有节点都收到信号？如果不能使所有节点收到信号，返回 -1。

注意:

  1. N 的范围在 [1, 100] 之间。
  2. K 的范围在 [1, N] 之间。
  3. times 的长度在 [1, 6000] 之间。
  4. 所有的边 times[i] = (u, v, w) 都有 1 <= u, v <= N 且 0 <= w <= 100。
Runtime: 496 ms
Memory Usage: 19.3 MB
 1 class Solution {
 2     func networkDelayTime(_ times: [[Int]], _ N: Int, _ K: Int) -> Int {
 3         var res:Int = 0
 4         var edges:[Int:[(Int,Int)]] = [Int:[(Int,Int)]]()
 5         var dist:[Int] = [Int](repeating:Int.max,count:N + 1)
 6         var q:[Int] = [K]
 7         dist[K] = 0
 8         for e in times
 9         {
10             edges[e[0],default:[(Int,Int)]()].append((e[1], e[2]))
11         }
12         while (!q.isEmpty)
13         {
14             var u:Int = q.first!
15             q.removeFirst()
16             var visited:Set<Int> = Set<Int>()
17             for (key,val) in edges[u,default:[(Int,Int)]()]
18             {
19                 var v:Int = key
20                 var w:Int = val
21                 if dist[u] != Int.max && dist[u] + w < dist[v]
22                 {
23                     dist[v] = dist[u] + w
24                     if visited.contains(v) {continue}
25                     visited.insert(v)
26                     q.append(v)
27                 }
28             }        
29         }
30         for i in 1...N
31         {
32             res = max(res, dist[i])        
33         }
34         return res == Int.max ? -1 : res
35     }
36 }

604ms

 1 class Solution {
 2         func networkDelayTime(_ times: [[Int]], _ N: Int, _ K: Int) -> Int {
 3         guard  times.count > 0 else {
 4             return -1
 5         }
 6         
 7         
 8         var graph = [[Int]](repeating:[Int](repeating:-1, count:N + 1), count: N + 1)
 9         
10         for t in times {
11             graph[t[0]][t[1]] = t[2]
12         }
13         
14         var memo = [Int: Int]()
15         var visited = [Int: Bool]()
16         //We need to use bfs
17         var queue = [Int]()
18         for i in 1...N {
19             queue.append(i)
20             memo[i] = Int.max
21         }
22         
23         memo[K] = 0
24         
25         while queue.count != 0 {
26             queue.sort(by:{ memo[$0]! < memo[$1]!  })
27             let node = queue.removeFirst()
28             visited[node] = true
29             
30             for i in 0..<graph[node].count {
31                 if visited[i] == true || graph[node][i] == -1 {
32                     continue
33                 } else {
34                     memo[i]! = min(memo[i]!, memo[node]! + graph[node][i])
35                 }
36             }
37         }
38         
39         var maxT = 0
40         
41         print(memo)
42             
43         
44         for i in 1...N {
45             if let time = memo[i] {
46                 if time == Int.max {
47                     return -1
48                 } else {
49                      maxT = max(maxT, time)
50                 }
51             }
52         }
53         
54         return maxT
55     }
56 }

660ms

 1 class Solution {
 2   func networkDelayTime(_ times: [[Int]], _ N: Int, _ K: Int) -> Int {
 3     var delayTimes = Array(repeating: Int.max, count: N + 1)
 4     delayTimes[K] = 0
 5     
 6     var nodeLeft = Array(repeating: 1, count: N + 1)
 7     
 8     while true {
 9       var closest = Int.max
10       var closestIndex = -1
11       for i in 1..<nodeLeft.count {
12         if nodeLeft[i] != 0 && delayTimes[i] < closest {
13           closest = delayTimes[i]
14           closestIndex = i
15         }
16       }
17       
18       if closestIndex == -1 {
19         break
20       }
21       
22       for i in 0..<times.count {
23         if times[i][0] == closestIndex {
24           delayTimes[times[i][1]] = min(delayTimes[times[i][1]], delayTimes[times[i][0]] + times[i][2])
25         }
26       }
27       
28       nodeLeft[closestIndex] = 0
29     }
30     
31     var delayTime = 0
32     
33     for i in 1..<delayTimes.count {
34       if delayTimes[i] == Int.max {
35         return -1
36       } else {
37         delayTime = max(delayTime, delayTimes[i])
38       }
39     }
40     
41     return delayTime
42   }
43 }

680ms

 1 class Solution {
 2   func networkDelayTime(_ times: [[Int]], _ N: Int, _ K: Int) -> Int {
 3     var delayTimes = Array(repeating: Int.max, count: N)
 4     delayTimes[K - 1] = 0
 5     
 6     var nodeLeft = Array(repeating: 1, count: N)
 7     
 8     while true {
 9       var closest = Int.max
10       var closestIndex = -1
11       for i in 0..<nodeLeft.count {
12         if nodeLeft[i] != 0 && delayTimes[i] < closest {
13           closest = delayTimes[i]
14           closestIndex = i + 1
15         }
16       }
17       
18       if closestIndex == -1 {
19         break
20       }
21       
22       for i in 0..<times.count {
23         if times[i][0] == closestIndex {
24           delayTimes[times[i][1] - 1] = min(delayTimes[times[i][1] - 1], delayTimes[times[i][0] - 1] + times[i][2])
25         }
26       }
27       
28       nodeLeft[closestIndex - 1] = 0
29     }
30     
31     return delayTimes.max()! == Int.max ? -1 : delayTimes.max()!
32   }
33 }

712ms

  1 class Solution {
  2     func networkDelayTime(_ times: [[Int]], _ N: Int, _ K: Int) -> Int {
  3     let graph = Graph<Int>(.undirected)
  4     times.forEach { (time) in
  5         let source = graph.createVertex(time[0])
  6         let destination = graph.createVertex(time[1])
  7         graph.addDirectedEdge(from: source, to: destination, weight: Double(time[2]))
  8     }
  9     
 10     var distances: [Vertex<Int>: Int] = [:]
 11     var parent: [Vertex<Int>: Vertex<Int>] = [:]
 12     dijstra(graph, source: graph.createVertex(K), distances: &distances, parent: &parent)
 13     if distances.count != N {
 14         return -1 
 15     }
 16     return distances.reduce(into: 0, { $0 = max($0, $1.value) })
 17 }
 18 
 19 
 20 func dijstra<T: Hashable>(_ graph: Graph<T>,
 21                           source: Vertex<T>,
 22                           distances: inout [Vertex<T>: Int],
 23                           parent: inout [Vertex<T>: Vertex<T>]
 24     ) {
 25     var source = source
 26     var inTree: Set<Vertex<T>> = []
 27     distances[source] = 0
 28     
 29     while !inTree.contains(source) {
 30         inTree.insert(source)
 31         
 32         for edge in graph.edges(of: source) {
 33             let destination = edge.destination
 34             let edgeWeight = Int(edge.weight!)
 35             if distances[destination] == nil ||
 36                 distances[destination]! > edgeWeight + distances[source]! {
 37                 distances[destination] = edgeWeight + distances[source]!
 38                 parent[destination] = source
 39             }
 40         }
 41         var minDistance = Int.max
 42         for (vertex, distance) in distances where !inTree.contains(vertex) {
 43             if minDistance > distance {
 44                 minDistance = distance
 45                 source = vertex
 46             }
 47         }
 48     }
 49     
 50 }
 51 }
 52 
 53 enum GraphType {
 54     case directed
 55     case undirected
 56 }
 57 
 58 
 59 struct Vertex<T:Hashable> : Hashable{
 60     public var val : T
 61     
 62     public init(_ val: T){
 63         self.val = val
 64     }
 65     
 66     public var hashValue: Int {
 67         return val.hashValue
 68     }
 69     
 70     public static func == (lhs: Vertex<T>, rhs: Vertex<T>) -> Bool{
 71         return lhs.val == rhs.val
 72     }
 73 }
 74 
 75 extension Vertex: CustomStringConvertible{
 76     var description: String{
 77         return "\(val)"
 78     }
 79 }
 80 
 81 
 82 struct Edge<T:Hashable>{
 83     public let source: Vertex<T>
 84     public let destination: Vertex<T>
 85     public var weight : Double?
 86 }
 87 
 88 class Graph<T: Hashable>{
 89     public var vertices : [Vertex<T>] = []
 90     private var adjacencyList : [Vertex<T> : [Edge<T>]] = [:]
 91     public var type: GraphType
 92     public init(_ type: GraphType) {
 93         self.type = type
 94     }
 95     
 96     public func createVertex(_ val: T)->Vertex<T>{
 97         let vertex = Vertex<T>.init(val)
 98         if adjacencyList[vertex] == nil{
 99             adjacencyList[vertex] = []
100             vertices.append(vertex)
101         }
102         return vertex
103     }
104     
105     public func addDirectedEdge(from source: Vertex<T>,
106                                 to destination: Vertex<T>,
107                                 weight: Double?
108         ){
109         let edge = Edge<T>.init(source: source, destination: destination, weight: weight)
110         adjacencyList[source]?.append(edge)
111     }
112     
113     public func addUndirectedEdge(between source: Vertex<T>,
114                                   and destination: Vertex<T>,
115                                   weight: Double?
116         ){
117         addDirectedEdge(from: source, to: destination, weight: weight)
118         addDirectedEdge(from: destination, to: source, weight: weight)
119     }
120     
121     public func edges(of source: Vertex<T>)->[Edge<T>]{
122         return adjacencyList[source] ?? []
123     }
124     
125     public func weight(of source: Vertex<T>,
126                        to destination: Vertex<T>
127         )->Double?{
128         return adjacencyList[source]?.first(where: {$0.destination == destination})?.weight
129     }
130 }

800ms

 1 class Solution {
 2     typealias link = (target: Int, delay: Int)
 3     
 4     private class node {
 5         var distance = Int.max
 6         var next = [link]()
 7     }
 8     
 9     func networkDelayTime(_ times: [[Int]], _ N: Int, _ K: Int) -> Int {
10         var dict = [Int:node]()
11         var visited = Set([K])
12         
13         for index in 1...N {
14             dict[index] = node()
15         }
16         
17         for time in times {
18             dict[time[0]]!.next.append((time[1],time[2]))
19         }
20         
21         dict[K]!.distance = 0
22         
23         while (visited.count != N) {
24             var shortestDist = Int.max; var shortestIndex = 0
25             for index in visited {
26                 let tmpNode = dict[index]!
27                 var counter = 0
28                 for connectedNodes in tmpNode.next {
29                     let tmpIndex = connectedNodes.target
30                     if visited.contains(tmpIndex) {
31                         _ = tmpNode.next.remove(at: counter)
32                         continue
33                     }
34                     counter += 1
35                     let tmpDist = connectedNodes.delay + tmpNode.distance
36                     let prevDist = dict[tmpIndex]!.distance
37                     
38                     if (tmpDist < prevDist) {
39                         dict[tmpIndex]!.distance = tmpDist
40                     }
41                     if (tmpDist < shortestDist) {
42                         shortestDist = tmpDist
43                         shortestIndex = tmpIndex
44                     }
45                 }
46             }
47             if (shortestIndex == 0) {
48                 return -1
49             }
50             visited.insert(shortestIndex)
51         }
52         
53         var maxDelay = 0
54         
55         for nodes in dict.values where (nodes.distance > maxDelay) {
56             maxDelay = nodes.distance
57         }
58         
59         return maxDelay
60     }
61 }

 

posted @ 2019-03-13 18:28  为敢技术  阅读(529)  评论(0)  编辑  收藏  举报