add: solution for pattern16 challenge2

Pattern16 - Topological Sort/Challenge2/solution.go

@@ -0,0 +1,75 @@
+package Challenge2
+
+/*
+* Minimum Height Trees
+We are given an undirected graph that has characteristics of a k-ary tree.
+In such a graph, we can choose any node as the root to make a k-ary tree.
+The root (or the tree) with the minimum height will be called Minimum Height Tree (MHT).
+There can be multiple MHTs for a graph.
+In this problem, we need to find all those roots which give us MHTs.
+Write a method to find all MHTs of the given graph and return a list of their roots.
+
+Input: vertices: 5, Edges: [[0, 1], [1, 2], [1, 3], [2, 4]]
+Output:[1, 2]
+Explanation: Choosing '1' or '2' as roots give us MHTs. In the below diagram, we can see that the
+height of the trees with roots '1' or '2' is three which is minimum.
+
+Input: vertices: 4, Edges: [[0, 1], [0, 2], [2, 3]]
+Output:[0, 2]
+Explanation: Choosing '0' or '2' as roots give us MHTs. In the below diagram, we can see that the
+height of the trees with roots '0' or '2' is three which is minimum.
+
+Input: vertices: 4, Edges: [[0, 1], [1, 2], [1, 3]]
+Output:[1]
+
+ref: https://leetcode-cn.com/problems/minimum-height-trees/
+*/
+
+func findMinHeightTrees(n int, edges [][]int) []int {
+	if n == 1 {
+		return []int{0}
+	}
+
+	var (
+		inDegree = make(map[int]int)
+		graph    = make(map[int][]int)
+	)
+	for i := 0; i < n; i++ {
+		inDegree[i] = 0
+		graph[i] = []int{}
+	}
+
+	for _, v := range edges {
+		n1, n2 := v[0], v[1]
+		graph[n1] = append(graph[n1], n2)
+		graph[n2] = append(graph[n2], n1)
+		inDegree[n1]++
+		inDegree[n2]++
+	}
+
+	leaves := make([]int, 0)
+	for k, v := range inDegree {
+		if v == 1 {
+			leaves = append(leaves, k)
+		}
+	}
+
+	totalNodes := n
+	for totalNodes > 2 {
+		leavesSize := len(leaves)
+		totalNodes -= leavesSize
+		for i := 0; i < leavesSize; i++ {
+			vertex := leaves[0]
+			leaves = leaves[1:]
+			children := graph[vertex]
+			for _, v := range children {
+				inDegree[v]--
+				if inDegree[v] == 1 {
+					leaves = append(leaves, v)
+				}
+			}
+		}
+	}
+
+	return leaves
+}

Pattern16 - Topological Sort/Challenge2/solution_test.go

@@ -0,0 +1,32 @@
+package Challenge2
+
+import (
+	"reflect"
+	"testing"
+)
+
+func Test_findMinHeightTrees(t *testing.T) {
+	type args struct {
+		n     int
+		edges [][]int
+	}
+	tests := []struct {
+		name string
+		args args
+		want []int
+	}{
+		{"case1", args{5, [][]int{{0, 1}, {1, 2}, {1, 3}, {2, 4}}}, []int{1, 2}},
+		{"case2", args{4, [][]int{{0, 1}, {0, 2}, {2, 3}}}, []int{0, 2}},
+		{"case3", args{4, [][]int{{0, 1}, {1, 2}, {1, 3}}}, []int{1}},
+		{"case4", args{6, [][]int{{3, 0}, {3, 1}, {3, 2}, {3, 4}, {5, 4}}}, []int{3, 4}},
+		{"case5", args{1, [][]int{}}, []int{0}},
+		{"case6", args{2, [][]int{{0, 1}}}, []int{0, 1}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := findMinHeightTrees(tt.args.n, tt.args.edges); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("findMinHeightTrees() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}