210. Schedule II - depth traversal

class Solution {
    
public:
    // It's the curriculum 207 An upgraded version of the question , The difference is that the results need to be output in an array 
    // Different places are marked , For those who don't understand the idea, it is suggested to turn to page 207 Notes to questions 
    vector<vector<int>> vecVecInt;
    vector<int> visited;
    bool flag = true;
    vector<int> ans;
    vector<int> findOrder(int numCourses, vector<vector<int>>& prerequisites) {
    
        visited.resize(numCourses);
        vecVecInt.resize(numCourses);
        for(auto i : prerequisites)
            vecVecInt[i[0]].push_back(i[1]);
        for(int i = 0; i < numCourses && flag; ++i){
    
            if(!visited[i]) // You have to add , Otherwise, the output will be repeated , And can improve efficiency 
                dfs(i);
        }
        if(flag)    // If you can finish all the courses , Output the answer 
            return ans;
        else    // Otherwise, return an empty array 
            return {
    };
    }
    void dfs(int n){
    
        visited[n] = 1;
        int size = vecVecInt[n].size();
        for(int i = 0; i < size; ++i){
    
            if(flag && visited[vecVecInt[n][i]] == 0){
    
                dfs(vecVecInt[n][i]);
                if(!flag)
                    return;
            }
            else if(visited[vecVecInt[n][i]] == 1){
    
                flag = false;
                return;
            }
        }
        visited[n] = 2;
        ans.push_back(n);   // Depth traversal , So just put it at the end 
    }
};

Accepted
44/44 cases passed (24 ms)
Your runtime beats 31.18 % of cpp submissions
Your memory usage beats 20.07 % of cpp submissions (14.2 MB)