【算法】【圖】拓撲排序

鄰接矩陣

#include <iostream>
#include <queue>
#include <algorithm>
#include <set>
using namespace std;

int n, m;

vector<int> topsort(vector<int>& inDegree, vector<vector<int>>& adj)
{
    queue<int> q;
    for(int i = 1; i < inDegree.size(); i++)
        if(!inDegree[i]) q.push(i);
        
    
    vector<int> res;
    while(!q.empty())
    {
        int cur = q.front();
        q.pop();
        res.push_back(cur);
        
        for(int i = 1; i <= n; i++)
        {
            if(adj[cur][i])
            {
                inDegree[i]--;
                if(inDegree[i] == 0) q.push(i);
            }
        }
    }
    return res.size() == n ? res : vector<int>();
}


int main()
{
    cin >> n >> m;
    vector<int> inDegree(n + 1, 0);
    vector<vector<int>> adj(n + 1, vector<int>(n + 1, 0));
    set<pair<int, int>> s;
    for(int i = 1; i <= m; i++)
    {
        int a, b;
        cin >> a >> b;
        adj[a][b] = 1;
        s.insert({a, b});
    }
    for(auto tmp : s)
        inDegree[tmp.second]++;
    vector<int> res = topsort(inDegree, adj);
    
    if(res.empty())
    {
        cout << -1 << endl;
        return 0;
    }
    for(auto & x : res)
        cout << x << " ";
    cout << endl;
    return 0;
}

鄰接表

class Solution {
public:

    bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
        vector<vector<int> > adj(numCourses);
        vector<int> inDrgree(numCourses, 0);
        for(auto tmp : prerequisites)
        {
            adj[tmp[1]].push_back(tmp[0]);
            inDrgree[tmp[0]]++;
        } 
        return topsort(inDrgree, adj);
    }




    bool topsort(vector<int>& inDrgree, vector<vector<int>> &adj)
    {
        queue<int> q;
        for(int i = 0; i < inDrgree.size(); i++)
            if(inDrgree[i] == 0) q.push(i);
        
        int cnt = 0;
        while(!q.empty())
        {
            int cur = q.front();
            q.pop();
            cnt++;
            for(auto &x : adj[cur])
            {
                inDrgree[x]--;
                if(inDrgree[x] == 0) q.push(x);
            }
        }

        return cnt == inDrgree.size();
    }
};