Add the initial EN translation for C++ code (#1346)

en/codes/cpp/chapter_graph/graph_bfs.cpp

@@ -0,0 +1,59 @@
+/**
+ * File: graph_bfs.cpp
+ * Created Time: 2023-03-02
+ * Author: krahets (krahets@163.com)
+ */
+
+#include "../utils/common.hpp"
+#include "./graph_adjacency_list.cpp"
+
+/* Breadth-first traversal */
+// Use adjacency list to represent the graph, to obtain all adjacent vertices of a specified vertex
+vector<Vertex *> graphBFS(GraphAdjList &graph, Vertex *startVet) {
+    // Vertex traversal sequence
+    vector<Vertex *> res;
+    // Hash set, used to record visited vertices
+    unordered_set<Vertex *> visited = {startVet};
+    // Queue used to implement BFS
+    queue<Vertex *> que;
+    que.push(startVet);
+    // Starting from vertex vet, loop until all vertices are visited
+    while (!que.empty()) {
+        Vertex *vet = que.front();
+        que.pop();          // Dequeue the vertex at the head of the queue
+        res.push_back(vet); // Record visited vertex
+        // Traverse all adjacent vertices of that vertex
+        for (auto adjVet : graph.adjList[vet]) {
+            if (visited.count(adjVet))
+                continue;            // Skip already visited vertices
+            que.push(adjVet);        // Only enqueue unvisited vertices
+            visited.emplace(adjVet); // Mark the vertex as visited
+        }
+    }
+    // Return the vertex traversal sequence
+    return res;
+}
+
+/* Driver Code */
+int main() {
+    /* Initialize undirected graph */
+    vector<Vertex *> v = valsToVets({0, 1, 2, 3, 4, 5, 6, 7, 8, 9});
+    vector<vector<Vertex *>> edges = {{v[0], v[1]}, {v[0], v[3]}, {v[1], v[2]}, {v[1], v[4]},
+                                      {v[2], v[5]}, {v[3], v[4]}, {v[3], v[6]}, {v[4], v[5]},
+                                      {v[4], v[7]}, {v[5], v[8]}, {v[6], v[7]}, {v[7], v[8]}};
+    GraphAdjList graph(edges);
+    cout << "\nAfter initialization, the graph is\n";
+    graph.print();
+
+    /* Breadth-first traversal */
+    vector<Vertex *> res = graphBFS(graph, v[0]);
+    cout << "\nBreadth-first traversal (BFS) vertex sequence is" << endl;
+    printVector(vetsToVals(res));
+
+    // Free memory
+    for (Vertex *vet : v) {
+        delete vet;
+    }
+
+    return 0;
+}