CF G. Orientation of Edges BFS

来两遍 $BFS,$ 都贪心一下即可.

#include <bits/stdc++.h>
#define maxn 300009
using namespace std;
void setIO(string s) {
    string in=s+".in";
    freopen(in.c_str(),"r",stdin);
}
queue<int>Q;
int n,m,s,edges,nn=0;
int hd[maxn],to[maxn<<1],nex[maxn<<1],val[maxn<<1],vis[maxn],mk[maxn<<1],idx[maxn<<1],ou[maxn<<1];
void addedge(int u,int v,int c) {
    nex[++edges]=hd[u],hd[u]=edges,to[edges]=v,val[edges]=c;
}
void solve1() {
    memset(vis,0,sizeof(vis));
    vis[s]=1;
    Q.push(s);
    while(!Q.empty()) {
        int u=Q.front();Q.pop();
        for(int i=hd[u];i;i=nex[i]) {
            int v=to[i];
            if(val[i]) {
                if(val[i]==1) ou[idx[i]]=0;
                else ou[idx[i]]=1;
                continue;
            }
            if(!vis[v]) {
                Q.push(v);
                vis[v]=1;
            }
        }
    }
    int cnt=0;
    for(int i=1;i<=n;++i) if(vis[i]) ++cnt;
    printf("%d\n",cnt);
    for(int i=1;i<=nn;++i) if(ou[i]) printf("+");  else printf("-");
    printf("\n");
}
void solve2() {
    memset(vis,0,sizeof(vis));
    vis[s]=1;
    Q.push(s);
    int cc=0;
    while(!Q.empty()) {
        int u=Q.front();Q.pop();
        for(int i=hd[u];i;i=nex[i]) {
            int v=to[i];
            if(!vis[v]) {
                Q.push(v);
                vis[v]=1;
                if(val[i])mk[i]=1;
            }
        }
    }
    int cnt=0;
    for(int i=1;i<=n;++i) if(vis[i]) ++cnt;
    printf("%d\n",cnt);
    for(int i=1;i<=edges;++i) {
        if(mk[i]==1) {
            if(val[i]==1) ou[idx[i]]=1;
            else ou[idx[i]]=0;
        }
    }
    for(int i=1;i<=nn;++i) if(ou[i]) printf("+"); else printf("-");
    printf("\n");
    memset(ou,0,sizeof(ou));
}
int main() {
    // setIO("input");
    scanf("%d%d%d",&n,&m,&s);
    for(int i=1;i<=m;++i) {
        int t,u,v;
        scanf("%d%d%d",&t,&u,&v);
        if(t==1) addedge(u,v,0);
        else addedge(u,v,1),idx[edges]=++nn,addedge(v,u,2),idx[edges]=nn;
    }
    solve2();
    solve1();
    return 0;
}