HDU 4280 Island Transport(网络流，SAP）

来源：互联网发布：mac 室内设计软件编辑：程序博客网时间：2024/05/29 09:13
解题思路：
建模很简单，不过以前一直用dinic，而这个题目数据偏大，用dinic超时了，据说没有可以卡住SAP的网络流，于是搞到了一套SAP的模版，过了，保存一下模版。
#include <iostream>#include <cstring>#include <cstdio>#include <cmath>#include <cstdlib>#include <vector>#include <queue>#include <stack>#include <map>#include <set>#pragma comment(linker, "/STACK:1024000000,1024000000")#define LL long long using namespace std;const int MAXN=100010;//点数的最大值const int MAXM=400010;//边数的最大值const int INF=0x3f3f3f3f;struct 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yint n;//n是总的点的个数，包括源点和汇点void init(){    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 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=INF;            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;        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;}int main(){    int T,N,M;    scanf("%d", &T);    while(T--)    {        scanf("%d%d", &N, &M);        int Min = 100010;        int Max = -100010;        int u,v,w;        n = N;        init();        int x, y;        int s,t;        for(int i=1;i<=N;i++)        {            scanf("%d%d", &x,&y);            if(x < Min)            {                Min = x;                s = i;            }            if(x > Max)            {                Max = x;                t = i;            }        }        for(int i=1;i<=M;i++)        {            scanf("%d%d%d", &u,&v,&w);            AddEdge(u,v,w);            AddEdge(v,u,w);        }        printf("%d\n", SAP(s,t));    }    return 0;}
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