Orientation of Edges CodeForces

n点，m边，一个点s，输入m条边，有单向边和双向边，决定双向边的方向使得和s相连的点最多/最少 题目链接
bfs做法：

#include<bits/stdc++.h>using namespace std;const int maxn = 5e5+7;struct node{    int u,v,id,next;}edge[2000000];int color[maxn];bool vis[maxn];int head[maxn],cnt;void addedge(int u,int v,int id){    edge[cnt].u = u;    edge[cnt].v =v;    edge[cnt].id= id;    edge[cnt].next = head[u];    head[u] =cnt++;}int bfs1(int u){    queue<int>o;    o.push(u);    memset(vis,0,sizeof(vis));    int ans = 0;    vis[u] = true;    ans++;    while(!o.empty())    {        int u = o.front();        o.pop();        for(int i=head[u];~i;i = edge[i].next)        {            int v= edge[i].v;            int id = edge[i].id;            if(vis[v])continue;            if(id!=-1)            {                color[id/2] = (id%2);                //取出时按照0，1，2，3，。。的形式取出                //并对2取余判断双向边的方向            }            o.push(v);            vis[v] = true;            ans++;        }    }    return ans;}int bfs2(int u){    queue<int>o;    o.push(u);    memset(vis,0,sizeof(vis));    int ans = 0;    ans++;    vis[u] = true;    while(!o.empty())    {        int u = o.front();        o.pop();        for(int i=head[u];~i;i = edge[i].next)        {            int v= edge[i].v;            int id = edge[i].id;            if(vis[v])continue;            if(id!=-1)            {                color[id/2] = 1^(id%2);                continue;                //求最小值时能联通的边一律取反，使其不联通            }            o.push(v);            vis[v] = true;            ans++;        }    }    return ans;}int main(){    int n,m,s;     cnt = 0;     memset(head,-1,sizeof(head));     int pos = 0;     scanf("%d%d%d",&n,&m,&s);     for(int i=1;i<=m;i++)     {         int op,u,v;         scanf("%d%d%d",&op,&u,&v);         if(op==1)         {             addedge(u,v,-1);         }         else         {             addedge(u,v,pos);             addedge(v,u,pos+1);             pos+=2;         }         //存储时按0,1, 2,3...的形式存储     }     int ans1 = bfs1(s);     cout<<ans1<<endl;     for(int i=0;i<pos/2;i++)     {         if(color[i])printf("-");         else printf("+");     }     cout<<endl;     int ans2   = bfs2(s);     cout<<ans2<<endl;          for(int i=0;i<pos/2;i++)     {         if(color[i])printf("-");         else printf("+");     }    return 0;}

dfs做法：

#include<bits/stdc++.h>using namespace std;const int maxn = 5e5+7;typedef pair<int,int> pa;vector<pa>G[maxn];int sum;int vis[maxn],ans[maxn],op[maxn];int u[maxn],v[maxn];void dfs1(int u){    if(vis[u])return;    vis[u] = 1;    sum++;    for(auto y: G[u])    {        if(op[y.second]==1)            dfs1(y.first);        else if(!ans[y.second])        {            if(v[y.second]==y.first)//双向边的正向                ans[y.second]  =1;            else ans[y.second] = 2;            dfs1(y.first);        }    }}void dfs2(int u){    if(vis[u])return;    vis[u] = 1;    sum++;    for(auto y: G[u])    {        if(op[y.second]==1)            dfs2(y.first);        else if(!ans[y.second])        {            if(v[y.second]==y.first)//双向边的正向                ans[y.second]  =2;            else ans[y.second] = 1;        }    }}int main(){    int n,m,s;    scanf("%d%d%d",&n,&m,&s);    for(int i=1; i<=m; i++)    {        scanf("%d%d%d",&op[i],&u[i],&v[i]);        G[u[i]].push_back(make_pair(v[i],i));        if(op[i]==2)            G[v[i]].push_back(make_pair(u[i],i));    }    memset(vis,0,sizeof(vis));    memset(ans,0,sizeof(ans));    sum = 0;    dfs1(s);    cout<<sum<<endl;    for(int i=1; i<=m; i++)    {        if(op[i]==2)        {            if(ans[i]==1)                printf("+");            else                printf("-");        }    }    cout<<endl;    memset(vis,0,sizeof(vis));    memset(ans,0,sizeof(ans));    sum = 0;    dfs2(s);    cout<<sum<<endl;    for(int i=1; i<=m; i++)    {        if(op[i]==2)        {            if(ans[i]==1)                printf("+");            else                printf("-");        }    }    cout<<endl;    return 0;}