hdu 6311 Cover

Posted 2021-01-07 lmissher

无向图的最小路径覆盖。

 

 

 

 

 

#include <bits/stdc++.h>
using namespace std;
const int M = 1e5+7;
int head[M],cnt,n,m,deg[M],tot,p[M<<2],vis[M],s;
vector<int> v,ans[M];
struct edge
{
    int v,next;
}e[M<<2];
void addedge(int u,int v){
    e[++cnt].v=v;e[cnt].next=head[u];
    head[u]=cnt;
}
void init(){
    for(int i=1;i<=n;i++) deg[i]=0,vis[i]=0,head[i]=-1;
    memset(p,0,sizeof(p));
    tot=cnt=0;
}
void dfs(int u){
    vis[u]=1;
    if(deg[u]%2!=0) v.push_back(u);
    for(int i=head[u];~i;i=e[i].next){
        int v=e[i].v;
        if(vis[v]) continue;
        dfs(v);
    }
    return ;
}
void dfs1(int u){
    for(int i=head[u];~i;i=e[i].next){
        if(!p[i]){
            int kk;
            if(i%2!=0) kk=i/2+1,p[i]=p[i+1]=1;
            else kk=-(i/2),p[i]=p[i-1]=1;
            dfs1(e[i].v);
            if(i>2*m)
                tot++;
            else ans[tot].push_back(kk);
        }
    }
}
int main(){
    while(~scanf("%d%d",&n,&m)){
        init();
        for(int i=1;i<=m;i++){
            int u,v;
            scanf("%d%d",&u,&v);
            addedge(u,v);addedge(v,u);
            deg[u]++,deg[v]++;
        }
        for(int i=1;i<=n;i++){
            if(!vis[i]&&deg[i]){
                v.clear();
                dfs(i);
                for(int i=2;i<v.size();i+=2){
                    addedge(v[i],v[i+1]);addedge(v[i+1],v[i]);
                }
                if(!v.size()) s=i;
                else s=v[0];
                dfs1(s);
                tot++;
            }
        }
        printf("%d
",tot);
        for(int i=0;i<tot;i++)
        {
            printf("%d ",ans[i].size());
            for(int j=0;j<ans[i].size();j++){
                printf("%d%c",-1*ans[i][j],j==ans[i].size()-1?‘
‘:‘ ‘);
            }
            ans[i].clear();
        }
    }
    return 0;
}

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