Add solution for Challenge 4 by yz4230

Author: yz4230

challenge-4/submissions/yz4230/solution-template.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"fmt"
+	"sync"
+)
+
+// ConcurrentBFSQueries concurrently processes BFS queries on the provided graph.
+// - graph: adjacency list, e.g., graph[u] = []int{v1, v2, ...}
+// - queries: a list of starting nodes for BFS.
+// - numWorkers: how many goroutines can process BFS queries simultaneously.
+//
+// Return a map from the query (starting node) to the BFS order as a slice of nodes.
+// YOU MUST use concurrency (goroutines + channels) to pass the performance tests.
+func ConcurrentBFSQueries(graph map[int][]int, queries []int, numWorkers int) map[int][]int {
+	// TODO: Implement concurrency-based BFS for multiple queries.
+	// Return an empty map so the code compiles but fails tests if unchanged.
+
+	if numWorkers <= 0 {
+		return nil
+	}
+
+	bfs := func(query int) []int {
+		visited := []int{}
+		visitedSet := map[int]struct{}{}
+		queue := []int{}
+		queue = append(queue, query)
+		for len(queue) > 0 {
+			entry := queue[0]
+			queue = queue[1:]
+			if _, ok := visitedSet[entry]; ok {
+				continue
+			}
+			visited = append(visited, entry)
+			visitedSet[entry] = struct{}{}
+			for _, adj := range graph[entry] {
+				queue = append(queue, adj)
+			}
+		}
+
+		return visited
+	}
+
+	type Task struct {
+		ID  int
+		Key int
+	}
+
+	type Result struct {
+		ID      int
+		Key     int
+		Visited []int
+	}
+
+	chTask := make(chan Task)
+	chResult := make(chan Result)
+	results := map[int][]int{}
+
+	wg := &sync.WaitGroup{}
+	for range numWorkers {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for task := range chTask {
+				chResult <- Result{
+					ID:      task.ID,
+					Key:     task.Key,
+					Visited: bfs(task.Key),
+				}
+			}
+		}()
+	}
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for idx, query := range queries {
+			chTask <- Task{ID: idx, Key: query}
+		}
+		close(chTask)
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for range len(queries) {
+			result := <-chResult
+			results[result.Key] = result.Visited
+		}
+		close(chResult)
+	}()
+
+	wg.Wait()
+
+	return results
+}
+
+func main() {
+	graph := map[int][]int{
+		0: {1, 2},
+		1: {2, 3},
+		2: {3},
+		3: {4},
+		4: {},
+	}
+	queries := []int{0, 1, 2}
+	numWorkers := 2
+
+	results := ConcurrentBFSQueries(graph, queries, numWorkers)
+	fmt.Println(results)
+}