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

en/codes/cpp/chapter_graph/CMakeLists.txt

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+add_executable(graph_bfs graph_bfs.cpp)
+add_executable(graph_dfs graph_dfs.cpp)
+# add_executable(graph_adjacency_list graph_adjacency_list.cpp)
+add_executable(graph_adjacency_list_test graph_adjacency_list_test.cpp)
+add_executable(graph_adjacency_matrix graph_adjacency_matrix.cpp)

en/codes/cpp/chapter_graph/graph_adjacency_list.cpp

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+/**
+ * File: graph_adjacency_list.cpp
+ * Created Time: 2023-02-09
+ * Author: what-is-me (whatisme@outlook.jp), krahets (krahets@163.com)
+ */
+
+#include "../utils/common.hpp"
+
+/* Undirected graph class based on adjacency list */
+class GraphAdjList {
+  public:
+    // Adjacency list, key: vertex, value: all adjacent vertices of that vertex
+    unordered_map<Vertex *, vector<Vertex *>> adjList;
+
+    /* Remove a specified node from vector */
+    void remove(vector<Vertex *> &vec, Vertex *vet) {
+        for (int i = 0; i < vec.size(); i++) {
+            if (vec[i] == vet) {
+                vec.erase(vec.begin() + i);
+                break;
+            }
+        }
+    }
+
+    /* Constructor */
+    GraphAdjList(const vector<vector<Vertex *>> &edges) {
+        // Add all vertices and edges
+        for (const vector<Vertex *> &edge : edges) {
+            addVertex(edge[0]);
+            addVertex(edge[1]);
+            addEdge(edge[0], edge[1]);
+        }
+    }
+
+    /* Get the number of vertices */
+    int size() {
+        return adjList.size();
+    }
+
+    /* Add edge */
+    void addEdge(Vertex *vet1, Vertex *vet2) {
+        if (!adjList.count(vet1) || !adjList.count(vet2) || vet1 == vet2)
+            throw invalid_argument("Vertex does not exist");
+        // Add edge vet1 - vet2
+        adjList[vet1].push_back(vet2);
+        adjList[vet2].push_back(vet1);
+    }
+
+    /* Remove edge */
+    void removeEdge(Vertex *vet1, Vertex *vet2) {
+        if (!adjList.count(vet1) || !adjList.count(vet2) || vet1 == vet2)
+            throw invalid_argument("Vertex does not exist");
+        // Remove edge vet1 - vet2
+        remove(adjList[vet1], vet2);
+        remove(adjList[vet2], vet1);
+    }
+
+    /* Add vertex */
+    void addVertex(Vertex *vet) {
+        if (adjList.count(vet))
+            return;
+        // Add a new linked list to the adjacency list
+        adjList[vet] = vector<Vertex *>();
+    }
+
+    /* Remove vertex */
+    void removeVertex(Vertex *vet) {
+        if (!adjList.count(vet))
+            throw invalid_argument("Vertex does not exist");
+        // Remove the vertex vet's corresponding linked list from the adjacency list
+        adjList.erase(vet);
+        // Traverse other vertices' linked lists, removing all edges containing vet
+        for (auto &adj : adjList) {
+            remove(adj.second, vet);
+        }
+    }
+
+    /* Print the adjacency list */
+    void print() {
+        cout << "Adjacency list =" << endl;
+        for (auto &adj : adjList) {
+            const auto &key = adj.first;
+            const auto &vec = adj.second;
+            cout << key->val << ": ";
+            printVector(vetsToVals(vec));
+        }
+    }
+};
+
+// See test case in graph_adjacency_list_test.cpp

en/codes/cpp/chapter_graph/graph_adjacency_list_test.cpp

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+/**
+ * File: graph_adjacency_list_test.cpp
+ * Created Time: 2023-02-09
+ * Author: what-is-me (whatisme@outlook.jp), krahets (krahets@163.com)
+ */
+
+#include "./graph_adjacency_list.cpp"
+
+/* Driver Code */
+int main() {
+    /* Initialize undirected graph */
+    vector<Vertex *> v = valsToVets(vector<int>{1, 3, 2, 5, 4});
+    vector<vector<Vertex *>> edges = {{v[0], v[1]}, {v[0], v[3]}, {v[1], v[2]},
+                                      {v[2], v[3]}, {v[2], v[4]}, {v[3], v[4]}};
+    GraphAdjList graph(edges);
+    cout << "\nAfter initialization, the graph is" << endl;
+    graph.print();
+
+    /* Add edge */
+    // Vertices 1, 2 i.e., v[0], v[2]
+    graph.addEdge(v[0], v[2]);
+    cout << "\nAfter adding edge 1-2, the graph is" << endl;
+    graph.print();
+
+    /* Remove edge */
+    // Vertices 1, 3 i.e., v[0], v[1]
+    graph.removeEdge(v[0], v[1]);
+    cout << "\nAfter removing edge 1-3, the graph is" << endl;
+    graph.print();
+
+    /* Add vertex */
+    Vertex *v5 = new Vertex(6);
+    graph.addVertex(v5);
+    cout << "\nAfter adding vertex 6, the graph is" << endl;
+    graph.print();
+
+    /* Remove vertex */
+    // Vertex 3 i.e., v[1]
+    graph.removeVertex(v[1]);
+    cout << "\nAfter removing vertex 3, the graph is" << endl;
+    graph.print();
+
+    // Free memory
+    for (Vertex *vet : v) {
+        delete vet;
+    }
+
+    return 0;
+}

en/codes/cpp/chapter_graph/graph_adjacency_matrix.cpp

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+/**
+ * File: graph_adjacency_matrix.cpp
+ * Created Time: 2023-02-09
+ * Author: what-is-me (whatisme@outlook.jp)
+ */
+
+#include "../utils/common.hpp"
+
+/* Undirected graph class based on adjacency matrix */
+class GraphAdjMat {
+    vector<int> vertices;       // Vertex list, elements represent "vertex value", index represents "vertex index"
+    vector<vector<int>> adjMat; // Adjacency matrix, row and column indices correspond to "vertex index"
+
+  public:
+    /* Constructor */
+    GraphAdjMat(const vector<int> &vertices, const vector<vector<int>> &edges) {
+        // Add vertex
+        for (int val : vertices) {
+            addVertex(val);
+        }
+        // Add edge
+        // Edges elements represent vertex indices
+        for (const vector<int> &edge : edges) {
+            addEdge(edge[0], edge[1]);
+        }
+    }
+
+    /* Get the number of vertices */
+    int size() const {
+        return vertices.size();
+    }
+
+    /* Add vertex */
+    void addVertex(int val) {
+        int n = size();
+        // Add new vertex value to the vertex list
+        vertices.push_back(val);
+        // Add a row to the adjacency matrix
+        adjMat.emplace_back(vector<int>(n, 0));
+        // Add a column to the adjacency matrix
+        for (vector<int> &row : adjMat) {
+            row.push_back(0);
+        }
+    }
+
+    /* Remove vertex */
+    void removeVertex(int index) {
+        if (index >= size()) {
+            throw out_of_range("Vertex does not exist");
+        }
+        // Remove vertex at `index` from the vertex list
+        vertices.erase(vertices.begin() + index);
+        // Remove the row at `index` from the adjacency matrix
+        adjMat.erase(adjMat.begin() + index);
+        // Remove the column at `index` from the adjacency matrix
+        for (vector<int> &row : adjMat) {
+            row.erase(row.begin() + index);
+        }
+    }
+
+    /* Add edge */
+    // Parameters i, j correspond to vertices element indices
+    void addEdge(int i, int j) {
+        // Handle index out of bounds and equality
+        if (i < 0 || j < 0 || i >= size() || j >= size() || i == j) {
+            throw out_of_range("Vertex does not exist");
+        }
+        // In an undirected graph, the adjacency matrix is symmetric about the main diagonal, i.e., satisfies (i, j) == (j, i)
+        adjMat[i][j] = 1;
+        adjMat[j][i] = 1;
+    }
+
+    /* Remove edge */
+    // Parameters i, j correspond to vertices element indices
+    void removeEdge(int i, int j) {
+        // Handle index out of bounds and equality
+        if (i < 0 || j < 0 || i >= size() || j >= size() || i == j) {
+            throw out_of_range("Vertex does not exist");
+        }
+        adjMat[i][j] = 0;
+        adjMat[j][i] = 0;
+    }
+
+    /* Print adjacency matrix */
+    void print() {
+        cout << "Vertex list = ";
+        printVector(vertices);
+        cout << "Adjacency matrix =" << endl;
+        printVectorMatrix(adjMat);
+    }
+};
+
+/* Driver Code */
+int main() {
+    /* Initialize undirected graph */
+    // Edges elements represent vertex indices
+    vector<int> vertices = {1, 3, 2, 5, 4};
+    vector<vector<int>> edges = {{0, 1}, {0, 3}, {1, 2}, {2, 3}, {2, 4}, {3, 4}};
+    GraphAdjMat graph(vertices, edges);
+    cout << "\nAfter initialization, the graph is" << endl;
+    graph.print();
+
+    /* Add edge */
+    // Indices of vertices 1, 2 are 0, 2 respectively
+    graph.addEdge(0, 2);
+    cout << "\nAfter adding edge 1-2, the graph is" << endl;
+    graph.print();
+
+    /* Remove edge */
+    // Indices of vertices 1, 3 are 0, 1 respectively
+    graph.removeEdge(0, 1);
+    cout << "\nAfter removing edge 1-3, the graph is" << endl;
+    graph.print();
+
+    /* Add vertex */
+    graph.addVertex(6);
+    cout << "\nAfter adding vertex 6, the graph is" << endl;
+    graph.print();
+
+    /* Remove vertex */
+    // Index of vertex 3 is 1
+    graph.removeVertex(1);
+    cout << "\nAfter removing vertex 3, the graph is" << endl;
+    graph.print();
+
+    return 0;
+}

en/codes/cpp/chapter_graph/graph_bfs.cpp

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+/**
+ * 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;
+}

en/codes/cpp/chapter_graph/graph_dfs.cpp

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+/**
+ * File: graph_dfs.cpp
+ * Created Time: 2023-03-02
+ * Author: krahets (krahets@163.com)
+ */
+
+#include "../utils/common.hpp"
+#include "./graph_adjacency_list.cpp"
+
+/* Depth-first traversal helper function */
+void dfs(GraphAdjList &graph, unordered_set<Vertex *> &visited, vector<Vertex *> &res, Vertex *vet) {
+    res.push_back(vet);   // Record visited vertex
+    visited.emplace(vet); // Mark the vertex as visited
+    // Traverse all adjacent vertices of that vertex
+    for (Vertex *adjVet : graph.adjList[vet]) {
+        if (visited.count(adjVet))
+            continue; // Skip already visited vertices
+        // Recursively visit adjacent vertices
+        dfs(graph, visited, res, adjVet);
+    }
+}
+
+/* Depth-first traversal */
+// Use adjacency list to represent the graph, to obtain all adjacent vertices of a specified vertex
+vector<Vertex *> graphDFS(GraphAdjList &graph, Vertex *startVet) {
+    // Vertex traversal sequence
+    vector<Vertex *> res;
+    // Hash set, used to record visited vertices
+    unordered_set<Vertex *> visited;
+    dfs(graph, visited, res, startVet);
+    return res;
+}
+
+/* Driver Code */
+int main() {
+    /* Initialize undirected graph */
+    vector<Vertex *> v = valsToVets(vector<int>{0, 1, 2, 3, 4, 5, 6});
+    vector<vector<Vertex *>> edges = {{v[0], v[1]}, {v[0], v[3]}, {v[1], v[2]},
+                                      {v[2], v[5]}, {v[4], v[5]}, {v[5], v[6]}};
+    GraphAdjList graph(edges);
+    cout << "\nAfter initialization, the graph is" << endl;
+    graph.print();
+
+    /* Depth-first traversal */
+    vector<Vertex *> res = graphDFS(graph, v[0]);
+    cout << "\nDepth-first traversal (DFS) vertex sequence is" << endl;
+    printVector(vetsToVals(res));
+
+    // Free memory
+    for (Vertex *vet : v) {
+        delete vet;
+    }
+
+    return 0;
+}