Leetcode 课程表 C++ 图的深度搜索和广度搜索练习

广度搜索（degree）

struct GraphNode{
    int label;
    vector<GraphNode*> neighbours;
    GraphNode(int x):label(x){};
};
class Solution {
public:
    bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
        vector<GraphNode*> graph;
        vector<int> degree;
        for(int i = 0 ; i < numCourses;i++){
            graph.push_back(new GraphNode(i));
            degree.push_back(0);
        }
        queue<GraphNode*> Q;
        for(int i = 0 ;i < prerequisites.size();i++){
            GraphNode* first = graph[prerequisites[i][0]];
            GraphNode* second = graph[prerequisites[i][1]];
            second->neighbours.push_back(first);
            degree[prerequisites[i][0]]++;
        }
        for(int i = 0 ;i < numCourses;i++){
            if(degree[i] == 0) Q.push(graph[i]);
        }
        while(!Q.empty()){
            for(int i = 0 ; i < Q.front()->neighbours.size();i++){
                degree[Q.front()->neighbours[i]->label]--;
                if(degree[Q.front()->neighbours[i]->label] == 0){
                    Q.push(Q.front()->neighbours[i]);
                }
            }
            Q.pop();
        }
        for(int i = 0 ; i < numCourses;i++){
            delete graph[i];
        }
        for(int i = 0 ;i < numCourses;i++){
            if(degree[i]) return false;
        }
        return true;
    }
};

深度搜索

struct GraphNode{
    int label;
    vector<GraphNode*> neighbours;
    GraphNode(int x):label(x){};
};
class Solution {
public:
    bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
            vector<GraphNode*> graph;
            vector<int> visit;
            for(int i = 0 ;i<numCourses;i++){
                graph.push_back(new GraphNode(i));
                visit.push_back(-1);
            }
            for(int i = 0; i < prerequisites.size();i++){
                graph[prerequisites[i][1]]->neighbours.push_back( graph[prerequisites[i][0]]);
            }
            for (int i = 0 ; i < numCourses;i++){
                if(visit[i] == -1 && DFS_graph(graph[i],visit) == false) return false ;
            }
            for(int i = 0 ;i < numCourses;i++){
                delete graph[i];
            }
            return true;
    }
    bool DFS_graph(GraphNode* node,vector<int>& visit){
        visit[node->label] = 0;
        for (int i = 0 ; i < node->neighbours.size();i++){
            if(visit[node->neighbours[i]->label] == -1){
                if(DFS_graph(node->neighbours[i],visit) == false){
                    return false;
                }
            }
            else if(visit[node->neighbours[i]->label] == 0) return false;
        }
        visit[node->label] = 1;
        return true;
    }
};