hdu4280（最大流）

 

传送门：Island Transport

题意：有N个岛屿 M条无向路 每个路有一最大允许的客流量，求从最西的那个岛屿最多能运用多少乘客到最东的那个岛屿。

分析：无向图正反都加弧，权值一样，这题点多，使用SAP优势大，点少时dinic好些。

 

dinic：8314ms

#pragma comment(linker,"/STACK:1024000000,1024000000")

#include <cstdio>

#include <cstring>

#include <string>

#include <cmath>

#include <limits.h>

#include <iostream>

#include <algorithm>

#include <queue>

#include <cstdlib>

#include <stack>

#include <vector>

#include <set>

#include <map>

#define LL long long

#define mod 100000000

#define inf 0x3f3f3f3f

#define eps 1e-6

#define N 100010

#define lson l,m,rt<<1

#define rson m+1,r,rt<<1|1

#define PII pair<int,int>

using namespace std;

inline int read()

{

    char ch=getchar();

    int x=0,f=1;

    while(ch>'9'||ch<'0'){if(ch=='-')f=-1;ch=getchar();}

    while(ch<='9'&&ch>='0'){x=x*10+ch-'0';ch=getchar();}

    return x*f;

}

int n,m,vs,vt,tot;

int pre[N],q[N],cur[N],h[N];

struct edge

{

    int v,w,next;

    edge(){}

    edge(int v,int w,int next):v(v),w(w),next(next){}

}e[N<<1];

void addedge(int u,int v,int w)

{

    e[tot]=edge(v,w,pre[u]);

    pre[u]=tot++;

    e[tot]=edge(u,w,pre[v]);

    pre[v]=tot++;

}

void init()

{

    memset(pre,-1,sizeof(pre));

    tot=0;

}

/*******************dinic************************/

int bfs()

{

    int head=0,tail=1;

    memset(h,-1,sizeof(h));

    q[0]=vs;h[vs]=0;

    while(head!=tail)

    {

        int u=q[head++];

        for(int i=pre[u];~i;i=e[i].next)

        {

            int v=e[i].v,w=e[i].w;

            if(w&&h[v]==-1)

            {

                h[v]=h[u]+1;

                q[tail++]=v;

            }

        }

    }

    return h[vt]!=-1;

}

int dfs(int u,int flow)

{

    if(u==vt)return flow;

    int used=0;

    for(int i=cur[u];~i;i=e[i].next)

    {

        int v=e[i].v,w=e[i].w;

        if(h[v]==h[u]+1)

        {

            w=dfs(v,min(flow-used,w));

            e[i].w-=w;e[i^1].w+=w;

            if(e[i].w)cur[u]=i;

            used+=w;

            if(used==flow)return flow;

        }

    }

    if(!used)h[u]=-1;

    return used;

}

int dinic()

{

    int res=0;

    while(bfs())

    {

        for(int i=1;i<=n;i++)cur[i]=pre[i];

        res+=dfs(vs,inf);

    }

    return res;

}

/********************dinic***********************/

void build()

{

    int u,v,w;

    int mx=-inf,mn=inf;

    n=read();m=read();

    for(int i=1;i<=n;i++)

    {

        u=read();v=read();

        if(u<mn)mn=u,vs=i;

        if(u>mx)mx=u,vt=i;

    }

    for(int i=1;i<=m;i++)

    {

        u=read();v=read();w=read();

        addedge(u,v,w);

    }

}

int main()

{

    int T;

    T=read();

    while(T--)

    {

        init();

        build();

        printf("%d\n",dinic());

    }

}

View Code

 

SAP：2917ms

#pragma comment(linker,"/STACK:1024000000,1024000000")

#include <cstdio>

#include <cstring>

#include <string>

#include <cmath>

#include <limits.h>

#include <iostream>

#include <algorithm>

#include <queue>

#include <cstdlib>

#include <stack>

#include <vector>

#include <set>

#include <map>

#define LL long long

#define mod 100000000

#define inf 0x3f3f3f3f

#define eps 1e-6

#define N 100010

#define lson l,m,rt<<1

#define rson m+1,r,rt<<1|1

#define PII pair<int,int>

using namespace std;

inline int read()

{

    char ch=getchar();

    int x=0,f=1;

    while(ch>'9'||ch<'0'){if(ch=='-')f=-1;ch=getchar();}

    while(ch<='9'&&ch>='0'){x=x*10+ch-'0';ch=getchar();}

    return x*f;

}

int n,m,vs,vt,tot,NV;

int head[N],gap[N],level[N],q[N];

struct edge

{

    int v,w,next;

    edge(){}

    edge(int v,int w,int next):v(v),w(w),next(next){}

}e[N<<1];

void addedge(int u,int v,int w)

{

    e[tot]=edge(v,w,head[u]);

    head[u]=tot++;

    e[tot]=edge(u,w,head[v]);

    head[v]=tot++;

}

void init()

{

    memset(head,-1,sizeof(head));

    tot=0;

}

/***************************SAP***********************/

void bfs(int vt)

{

    memset(level,-1,sizeof(level));

    memset(gap,0,sizeof(gap));

    level[vt]=0;

    gap[level[vt]]++;

    queue<int>que;

    que.push(vt);

    while(!que.empty()) {

        int u=que.front();

        que.pop();

        for(int i=head[u]; i!=-1; i=e[i].next) {

            int v=e[i].v;

            if(level[v]!=-1)continue;

            level[v]=level[u]+1;

            gap[level[v]]++;

            que.push(v);



        }

    }

}

int pre[N];

int cur[N];

int SAP()

{

    bfs(vt);

    memset(pre,-1,sizeof(pre));

    memcpy(cur,head,sizeof(head));

    int u=pre[vs]=vs,flow=0,aug=inf;

    gap[0]=NV;

    while(level[vs]<NV) {

        bool flag=false;

        for(int &i=cur[u]; i!=-1; i=e[i].next) {

            int v=e[i].v;

            if(e[i].w&&level[u]==level[v]+1) {

                flag=true;

                pre[v]=u;

                u=v;

                aug=min(aug,e[i].w);

                if(v==vt) {

                    flow+=aug;

                    for(u=pre[v]; v!=vs; v=u,u=pre[u]) {

                        e[cur[u]].w-=aug;

                        e[cur[u]^1].w+=aug;

                    }

                    aug=inf;

                }

                break;

            }

        }

        if(flag)continue;

        int minlevel=NV;

        for(int i=head[u]; i!=-1; i=e[i].next) {

            int v=e[i].v;

            if(e[i].w&&level[v]<minlevel) {

                minlevel=level[v];

                cur[u]=i;

            }

        }

        if(--gap[level[u]]==0)break;

        level[u]=minlevel+1;

        gap[level[u]]++;

        u=pre[u];

    }

    return flow;

}

/**************************SAP**********************/

void build()

{

    int u,v,w;

    int mx=-inf,mn=inf;

    n=read();m=read();

    NV=n+1;

    for(int i=1;i<=n;i++)

    {

        u=read();v=read();

        if(u<mn)mn=u,vs=i;

        if(u>mx)mx=u,vt=i;

    }

    for(int i=1;i<=m;i++)

    {

        u=read();v=read();w=read();

        addedge(u,v,w);

    }

}

int main()

{

    int T;

    T=read();

    while(T--)

    {

        init();

        build();

        printf("%d\n",SAP());

    }

}

View Code