[Swift]LeetCode310. 最小高度树 | Minimum Height Trees_app

概述For an undirected graph with tree characteristics, we can choose any node as the root. The result graph is then a rooted tree. Among all possible rooted trees, those with minimum height are called min

For an undirected graph with tree characteristics,we can choose any node as the root. The result graph is then a rooted tree. Among all possible rooted trees,those with minimum height are called minimum height trees (MHTs). Given such a graph,write a function to find all the MHTs and return a List of their root labels.

Format
The graph contains n nodes which are labeled from 0 to n - 1. You will be given the number n and a List of undirected edges (each edge is a pair of labels).

You can assume that no duplicate edges will appear in edges. Since all edges are undirected, [0,1] is the same as [1,0] and thus will not appear together in edges.

Example 1 :

input:,0        |        1       /       2   3 Output: n = 4edges = [[1,0],[1,2],3]][1]

Example 2 :

input:,0  1  2      \ | /        3        |        4        |        5 Output: n = 6edges = [[0,3],[2,[4,[5,4]][3,4]

Note:

According to the definition of tree on Wikipedia: “a tree is an undirected graph in which any two vertices are connected by exactly one path. In other words,any connected graph without simple cycles is a tree.” The height of a rooted tree is the number of edges on the longest downward path between the root and a leaf.

对于一个具有树特征的无向图，我们可选择任何一个节点作为根。图因此可以成为树，在所有可能的树中，具有最小高度的树被称为最小高度树。给出这样的一个图，写出一个函数找到所有的最小高度树并返回他们的根节点。

格式

该图包含 n 个节点，标记为 0 到 n - 1。给定数字 n 和一个无向边 edges 列表（每一个边都是一对标签）。

你可以假设没有重复的边会出现在 edges 中。由于所有的边都是无向边， [0,1]和 [1,0] 是相同的，因此不会同时出现在 edges 里。

示例 1:

输入:,0        |        1       /       2   3 输出: n = 4edges = [[1,3]][1]

示例 2:

输入:,0  1  2      \ | /        3        |        4        |        5 输出: n = 6edges = [[0,4]

说明:

根据树的定义，树是一个无向图，其中任何两个顶点只通过一条路径连接。换句话说，一个任何没有简单环路的连通图都是一棵树。树的高度是指根节点和叶子节点之间最长向下路径上边的数量。

1724 ms

 1 class Solution { 2     func findMinHeightTrees(_ n: Int,_ edges: [[Int]]) -> [Int]{ 3         var graph = [Int : Set<Int>]() 4         for edge in edges { 5             if graph[edge[0]] == nil { 6                 graph[edge[0]] = [edge[1]] 7             }else { 8                 graph[edge[0]]!.insert(edge[1]) 9             }10             if graph[edge[1]] == nil {11                 graph[edge[1]] = [edge[0]]12             }else {13                 graph[edge[1]]!.insert(edge[0])14             }15             16         }17         while graph.count > 2 {18             let List = graph.filter{$1.count == 1}19             for dict in List {20                 graph[dict.value.first!]?.remove(dict.key)21                 graph[dict.key] = nil22             }23         }24         25         let res = Array(graph.keys)26         if res.isEmpty {27             return [0]28         }29         return res30     }31 }