CodeChef ROBOTDAG Robots in a DAG

SAP板子

#include<cstdio>#include<cstring>#include<queue>#include<iostream>#include<algorithm>using namespace std;const int MAXN=200007;const int oo=0x3f3f3f3f;const int MAXM=2000007;//边数的最大值typedef long long LL;const LL loo=4223372036854775807ll;typedef long double LB;const LL mod=1e9+7;struct Edge{    int from, to;    Edge(){}    Edge(int _a, int _b) { from=_a, to=_b; }};vector<Edge> G;//sapstruct Node{    int from, to, next;    int cap;}edge[MAXM];int tol;int head[MAXN];int dep[MAXN];int gap[MAXN];//gap[x]=y :说明残留网络中dep[i]==x的个数为ystruct SAP{    int n;//n是总的点的个数，包括源点和汇点    void init(int _n)    {        n=_n;        tol=0;        memset(head, -1, sizeof(head));    }    void addedge(int u, int v, int w)    {        edge[tol].from=u;        edge[tol].to=v;        edge[tol].cap=w;        edge[tol].next=head[u];        head[u]=tol++;        edge[tol].from=v;        edge[tol].to=u;        edge[tol].cap=0;        edge[tol].next=head[v];        head[v]=tol++;    }    void BFS(int start, int end)    {        memset(dep, -1, sizeof(dep));        memset(gap, 0, sizeof(gap));        gap[0]=1;        int que[MAXN];        int front, rear;        front=rear=0;        dep[end]=0;        que[rear++]=end;        while(front!=rear)        {            int u=que[front++];            if(front==MAXN)front=0;            for(int i=head[u];i!=-1;i=edge[i].next)            {                int v=edge[i].to;                if(dep[v]!=-1)continue;                que[rear++]=v;                if(rear==MAXN)rear=0;                dep[v]=dep[u]+1;                ++gap[dep[v]];            }        }    }    int sap(int start, int end, int k)//这里加了限制，流超过k就直接返回，为了加快速度    {        int res=0;        BFS(start, end);        int cur[MAXN];        int S[MAXN];        int top=0;        memcpy(cur, head, sizeof(head));        int u=start;        int i;        while(dep[start]<n)        {            if(u==end)            {                int temp=oo;                int inser;                for(i=0;i<top;i++)                    if(temp>edge[S[i]].cap)                    {                        temp=edge[S[i]].cap;                        inser=i;                    }                for(i=0;i<top;i++)                {                    edge[S[i]].cap-=temp;                    edge[S[i]^1].cap+=temp;                }                res+=temp;                top=inser;                u=edge[S[top]].from;            }            if(u!=end&&gap[dep[u]-1]==0)//出现断层，无增广路                break;            if(res>=k) break;//流大于k直接返回            for(i=cur[u];i!=-1;i=edge[i].next)                if(edge[i].cap!=0&&dep[u]==dep[edge[i].to]+1)                    break;            if(i!=-1)            {                cur[u]=i;                S[top++]=i;                u=edge[i].to;            }            else            {                int min=n;                for(i=head[u];i!=-1;i=edge[i].next)                {                    if(edge[i].cap==0)continue;                    if(min>dep[edge[i].to])                    {                        min=dep[edge[i].to];                        cur[u]=i;                    }                }                --gap[dep[u]];                dep[u]=min+1;                ++gap[dep[u]];                if(u!=start)u=edge[S[--top]].from;            }        }        return res;    }}isap;int main(){    int T;scanf("%d", &T);    while(T--)    {        int n, m, k;        scanf("%d%d%d", &n, &m, &k);        G.clear();        for(int i=0;i<m;i++)        {            int a, b;scanf("%d%d", &a, &b);            G.push_back(Edge(a, b));        }        int l=2, r=m+1;        int ans=-1;        while(l<=r)        {            int mid=(l+r)>>1;            const int super_t=(n*mid+1);            isap.init(n*mid+1);            for(Edge e : G)            {                int u=e.from, v=e.to;                for(int j=1;j<mid;j++)                    isap.addedge(u+(j-1)*n, v+j*n, 1);            }            for(int j=1;j<=mid;j++)            {                isap.addedge(j*n, super_t, oo);            }            int flow=isap.sap(1, super_t, k);            if(flow>=k)            {                r=mid-1, ans=mid-1;            }            else                l=mid+1;        }        printf("%d\n", ans);    }    return 0;}