初涉網路流 POJ 1459 Power Network

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怒搞一下午網路流，又去我一塊心病。

從2F到SAP再到Dinic終於過掉了。可是書上說Dinic的時間複雜度為v*v*e。感覺也應該逾時的啊，可是過掉了，好詭異。

後兩種演算法都是在第一種的基礎上進行最佳化。第一種方法就是不停的尋找增廣路，後兩種引進了層次網路的概念，第三種又改善了尋找增廣路的方法。

現在只能理解到這裡了。。。

#include <algorithm>#include <iostream>#include <cstring>#include <cstdlib>#include <cstdio>#include <queue>#include <cmath>#include <stack>#include <map>#pragma comment(linker, "/STACK:1024000000");#define EPS (1e-8)#define LL long long#define ULL unsigned long long#define _LL __int64#define _INF 0x3f3f3f3f#define Mod 6000007using namespace std;struct E{    int u,v,Max,now,next;}edge[30000];int Top;int head[300];void Link(int u,int v,int w){    edge[Top].u = u;    edge[Top].v = v;    edge[Top].Max = w;    edge[Top].now = 0;    edge[Top].next = head[u];    head[u] = Top++;}struct P{    int pre,now,floor;    bool mark;}sta[300];void Modify(int a,int t){    while(t != 1)    {        edge[sta[t].pre].now += a;        t = edge[sta[t].pre].u;    }}int SAP(int s,int t,int n){    for(int i = 1;i <= n; ++i)        sta[i].mark = false;    queue<int> q;    q.push(s);    sta[s].mark = true;    sta[s].now = 2000000000;    sta[s].pre = -1;    while(q.empty() == false)    {        if(sta[t].mark && sta[t].now)        {            Modify(sta[t].now,t);            return sta[t].now;        }        int f = q.front();        q.pop();        for(int p = head[f];p != -1; p = edge[p].next)        {            if(sta[edge[p].v].mark == false && sta[edge[p].u].floor == sta[edge[p].v].floor-1 && sta[edge[p].u].floor < sta[t].floor)            {                sta[edge[p].v].now = min(sta[f].now,edge[p].Max - edge[p].now);                if(sta[edge[p].v].now == 0)                    continue;                sta[edge[p].v].pre = p;//記錄邊的儲存位置                sta[edge[p].v].mark = true;                q.push(edge[p].v);            }        }    }    return 0;}void Updata_Floor(int s,int t,int n){    queue<int> q;    for(int i = 0;i <= n; ++i)        sta[i].mark = false,sta[i].floor = n;    q.push(s);    sta[s].mark = true;    sta[s].floor = 1;    while(q.empty() == false)    {        int f = q.front();        q.pop();        if(sta[t].mark && sta[t].floor <= sta[f].floor)            return ;        for(int p = head[f];p != -1; p = edge[p].next)        {            if(sta[edge[p].v].mark == false && edge[p].now < edge[p].Max)            {                sta[edge[p].v].mark = true;                sta[edge[p].v].floor = sta[f].floor + 1;                q.push(edge[p].v);            }        }    }}int dfs(int s,int t,int a){    if(s == t)        return a;    int f = 0;    for(int p = head[s],temp = 0;p != -1; p = edge[p].next)    {        if((sta[edge[p].v].floor < sta[t].floor || edge[p].v == t) && sta[edge[p].v].floor == sta[s].floor+1 && edge[p].now < edge[p].Max)        {            temp = dfs(edge[p].v,t,min(a-f,edge[p].Max-edge[p].now));            edge[p].now += temp;            f += temp;        }    }    return f;}int Dinic(int s,int t,int n){    return dfs(s,t,200000000);}int Cal_Max_Flow(int s,int t,int n){    int temp,f = 0;    do    {        Updata_Floor(s,t,n);        //temp = SAP(s,t,n);        temp = Dinic(s,t,n);        f += temp;    }while(temp);    return f;}int main(){    char s[50];    int i,n,np,nc,m,u,v,w;    while(scanf("%d %d %d %d",&n,&np,&nc,&m) != EOF)    {        memset(head,-1,sizeof(head));        Top = 0;        for(i = 0;i < m; ++i)        {            scanf("%s",s);            sscanf(s,"(%d,%d)%d",&u,&v,&w);            Link(u+2,v+2,w);        }        for(i = 0;i < np; ++i)        {            scanf("%s",s);            sscanf(s,"(%d)%d",&u,&w);            Link(1,u+2,w);       }        for(i = 0;i < nc; ++i)        {            scanf("%s",s);            sscanf(s,"(%d)%d",&u,&w);            Link(u+2,n+2,w);        }        printf("%d\n",Cal_Max_Flow(1,n+2,n+2));    }    return 0;}