add: Minimum Height Trees

Author: hijiangtao

README.md

@@ -53,6 +53,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 |210|[Course Schedule II](https://leetcode.com/problems/course-schedule-ii/) | [JavaScript](./src/course-schedule-ii/res.js)|Medium|
 |240|[Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/) | [JavaScript](./src/search-a-2d-matrix-ii/res.js)|Medium|
 |307|[Range Sum Query - Mutable](https://leetcode.com/problems/range-sum-query-mutable/) | [JavaScript](./src/range-sum-query-mutable/res.js)|Medium|
+|310|[Minimum Height Trees](https://leetcode.com/problems/minimum-height-trees/) | [JavaScript](./src/minimum-height-trees/res.js)|Medium|
 |342|[Power of Four](https://leetcode.com/problems/power-of-four/) | [JavaScript](./src/power-of-four/res.js)|Easy|
 |344|[Reverse String](https://leetcode.com/problems/reverse-string/) | [JavaScript](./src/reverse-string/res.js)|Easy|
 |371|[Sum of Two Integers](https://leetcode.com/problems/sum-of-two-integers/) | [JavaScript](./src/sum-of-two-integers/res.js)|Easy|

src/minimum-height-trees/res.js

@@ -0,0 +1,80 @@
+/**
+ * res.js
+ * @authors Joe Jiang (hijiangtao@gmail.com)
+ * @date    2017-04-17 14:02:24
+ * 
+ * For a 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.
+ * 
+ * Note:
+ * 
+ * (1) 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.”
+ * 
+ * (2) The height of a rooted tree is the number of edges on the longest downward path between the root and a leaf.
+ * 
+ * @param {number} n
+ * @param {number[][]} edges
+ * @return {number[]}
+ */
+let findMinHeightTrees = function(n, edges) {
+	let elen = edges.length, // 边数长度
+		nlist = [], // 节点列表
+		deglist = [], //度数列表
+		adj = new Array(n); //存储连边信息
+
+	for (let i = 0; i < n; i++) {
+		nlist.push(i);
+		deglist.push(0);
+		adj[i] = new Set();
+	}
+	for (let i = 0; i < elen; i++) {
+		let source = edges[i][0],
+			target = edges[i][1];
+
+		adj[source].add(target);
+		adj[target].add(source);
+		deglist[source]++;
+		deglist[target]++;
+	}
+
+	// 结果中只能是一个元素或者两个元素, 或者全部元素 (如果有多个树结构)
+	while (nlist.length > 2) {
+		let lenNow = nlist.length,
+			dellist = [];
+
+		for (let i = 0; i < lenNow; i++) {
+			let node = nlist[i];
+			if (!deglist[node]) {
+				//当前节点边数为0
+				nlist.splice(i--, 1);
+				lenNow--;
+			} else if (deglist[node] === 1) {
+				//删除边并减少两端节点的degree
+				let anothernode = -1;
+				for (let j = 0; j < lenNow; j++) {
+					if (i === j) continue;
+					if (adj[node].has(nlist[j])) {
+						anothernode = nlist[j];
+						break;
+					}
+				}
+				adj[node].delete(anothernode);
+				adj[anothernode].delete(node);
+				dellist.push(anothernode);
+				deglist[node] = 0;
+				nlist.splice(i--, 1);
+				lenNow--;
+			}
+		}
+
+		for (let i = dellist.length - 1; i >= 0; i--) {
+			deglist[dellist[i]]--;
+		}
+	}
+
+	return nlist;
+};