拓扑排序

#include"iostream"#include"stack"#include"vector"using namespace std;vector< vector<int> > G;//采用邻接表保存图vector<int> degree;     //度数表vector<int> is_in_stack;//判断是否入过栈vector<int> ans;        //保存答案int n,m;                //点数 弧数int topo_sort(){    stack<int> st;    for(int i=1;i<=n;i++){  //先找到入度为0的点 压入栈中        if(degree[i]==0){            st.push(i);            is_in_stack[i] = 1; //更新点的标志        }    }    while(!st.empty()){         int now = st.top();st.pop();        ans.push_back(now);        for(int i=0;i<G[now].size();i++){//把邻接的点的度数更新            degree[G[now][i]]--;        }        for(int i=1;i<=n;i++){            if(degree[i]==0&&!is_in_stack[i]){//把更新之后的图中入度为0的点入栈                st.push(i);                is_in_stack[i]=1;            }        }    }}int main(){    cin>>n>>m;    G.resize(n+1);    is_in_stack.resize(n+1);    degree.resize(n+1);    for(int i=0;i<m;i++){        int st,ed;        cin>>st>>ed;        G[st].push_back(ed);    }    for(int i=1;i<=n;i++){        is_in_stack[i]=0;        for(int j=0;j<G[i].size();j++){            degree[G[i][j]]++;        }    }    topo_sort();    int first = 1;    for(int i=0;i<ans.size();i++){        if(first) {first = 0;cout<<ans[i];}        else cout<<"--->"<<ans[i];    }    cout<<endl;    return 0;}/*6 81 21 31 43 23 54 56 46 5*/