✨ (connected-undirect-node): golang with adjacency map with dfs

go/graphs/0010-number-of-connected-components-in-an-undirected-graph/solution.go

@@ -1,6 +1,36 @@
 package main
 
 func Solve(n int, edges [][]int) int {
-	// TODO(scaffold): implement, then delete this line
-	panic("not implemented")
+	// 1 建立 adjacency list 來紀錄每個節點相連的狀況
+	// 2 透過 DFS 逐個節點透過 adjacency list 來走訪節點，只要每次走完就把 counter 加一
+	adjacencyMap := make(map[int][]int, n)
+	for _, edge := range edges {
+		adjacencyMap[edge[0]] = append(adjacencyMap[edge[0]], edge[1])
+		adjacencyMap[edge[1]] = append(adjacencyMap[edge[1]], edge[0])
+	}
+	// 紀錄走訪過得
+	visited := make(map[int]struct{}, n)
+
+	var dfs func(node int)
+	dfs = func(node int) {
+		if _, ok := visited[node]; ok {
+			return
+		}
+		visited[node] = struct{}{}
+		adjacencyNodes := adjacencyMap[node]
+		for _, adjacencyNode := range adjacencyNodes {
+			if _, ok := visited[adjacencyNode]; !ok {
+				dfs(adjacencyNode)
+			}
+		}
+	}
+
+	result := 0
+	for i := 0; i < n; i++ {
+		if _, ok := visited[i]; !ok {
+			dfs(i)
+			result++
+		}
+	}
+	return result
 }