Uva-1440-Inspection (only the minimum network flow of the Lower Bound)

Inspection

 

Question:

The question is still a bare network least flow problem with no upper bound and only the lower bound. The output path is too annoying .! I don't want to write any more. Give others' code.

 

Algorithm analysis:

The minimum network flow is generally determined by binary lookup. Note that the maximum stream must be called at the end of the output path. Because the traffic that has ended earlier is not necessarily the traffic of the final answer.

 

#include<cstdio>#include<cstring>#include<iostream>#include<queue>using namespace std;const int inf=1<<29;const int maxn=130;const int maxm=maxn*maxn*3;int n,e,st,s_st,s_des,des,head[maxn],nxt[maxm],pnt[maxm],flow[maxm],level[maxn];int c_in[maxn],c_out[maxn],out[maxn];bool go[maxn][maxn];queue<int> q;void AddEdge(int u,int v,int f){    //printf("Add %d %d %d\n",u,v,f);    pnt[e]=v;nxt[e]=head[u];flow[e]=f;head[u]=e++;    pnt[e]=u;nxt[e]=head[v];flow[e]=0;head[v]=e++;}bool BFS(){    memset(level,0,sizeof(level));    level[st]=1;    q.push(st);    while(!q.empty())    {        int u=q.front();        q.pop();        for(int i=head[u];i!=-1;i=nxt[i])            if(flow[i]&&!level[pnt[i]])            {                level[pnt[i]]=level[u]+1;                q.push(pnt[i]);            }    }    return level[des];}int DFS(int u,int maxf){    if(u==des||!maxf)        return maxf;    for(int i=head[u],t;i!=-1;i=nxt[i])        if(level[pnt[i]]==level[u]+1&&(t=DFS(pnt[i],min(maxf,flow[i]))))        {            flow[i]-=t;            flow[i^1]+=t;            return t;        }    return level[u]=0;}int maxflow(int s,int t){    st=s;des=t;    int ans=0;    while(BFS())        while(1)        {            int val=DFS(st,inf);            if(!val)                break;            ans+=val;        }    return ans;}bool check(int val){    e=st=0,des=n+1,s_st=n+2,s_des=n+3;    memset(head,-1,sizeof(head));    for(int i=1;i<=n;i++)        for(int j=1;j<=n;j++)            if(go[i][j])                AddEdge(i,j,inf);    for(int i=1;i<=n;i++)    {        AddEdge(st,i,inf);        AddEdge(i,des,inf);    }    AddEdge(des,st,val);    int sum=0;    for(int i=1;i<=n;i++)    {        if(c_in[i]>c_out[i])        {            AddEdge(s_st,i,c_in[i]-c_out[i]);            sum+=c_in[i]-c_out[i];        }        if(c_in[i]<c_out[i])            AddEdge(i,s_des,c_out[i]-c_in[i]);    }    int f=maxflow(s_st,s_des);    return f==sum;}int cap[maxn][maxn];int dfs(int u,int cnt){    out[cnt]=u;    if(u==des)    {        for(int i=1;i<cnt;i++)            printf("%d%c",out[i],i==cnt-1?'\n':' ');        return 1;    }    for(int i=1;i<=des;i++)        if(cap[u][i])        {            cap[u][i]--;            if(dfs(i,cnt+1))                return 1;        }    return 0;}void solve(){    int sl=0,sr=inf,ans=0;    while(sl<=sr)    {        int mid=(sl+sr)>>1;        if(check(mid))        {            sr=mid-1;                    ans=mid;        }        else            sl=mid+1;    }    printf("%d\n",ans);    check(ans);    st=0;des=n+1;    for(int i=1;i<=n;i++)        cap[st][i]=cap[i][des]=1;    for(int u=0;u<=n;u++)        for(int i=head[u];i!=-1;i=nxt[i])            if(cap[u][pnt[i]])                cap[u][pnt[i]]=flow[i^1]+1-(u==st||pnt[i]==des);    for(int i=1;i<=des;i++)        while(cap[st][i])        {            cap[st][i]--;            dfs(i,1);        }}int main(){    while(scanf("%d",&n)!=EOF)    {        memset(c_in,0,sizeof(c_in));        memset(c_out,0,sizeof(c_out));        memset(go,0,sizeof(go));        for(int i=1;i<=n;i++)        {            int m;            scanf("%d",&m);            for(int j=0;j<m;j++)            {                int v;                scanf("%d",&v);                go[i][v]=1;                cap[i][v]=1;                c_out[i]++;                c_in[v]++;            }        }        solve();    }    return 0;}

 

 

 

Uva-1440-Inspection (only the minimum network flow of the Lower Bound)