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;    
}