poj1459Power Network(最大流)

题目请戳这里

题目大意：好难读的题目。。有n个点，编号0~n-1，每个点可能是发电站，中转站或者用户。发电站i可以发pi的电，最大pmax，用户i消耗ci的电，最大cmax，中转站不发电也不消耗电。每两个站点之间有一条边，边权L，表示这条边最多能送L的电。求所有用户消耗最大的电量。

题目分析：网络流。需要增加一个源点和汇点。发电站是供电者，所以对于每个发电站，源点与其建一条边，边权为该发电站最大发电量。消费者耗电，对于每个消费者，与汇点建一条边，边权为消费者最大耗电量。然后将题目中给定的边加入到图中，跑一遍最大流即可。

详情请见代码：

#include <iostream>#include<cstdio>#include<cstring>#include<algorithm>using namespace std;const int N = 105;const int M = 310005;const int inf = 0x3f3f3f3f;int n,m,np,nc,num;int head[N];struct node{    int to,next,c,pre;}arc[M];short int que[N],cnt[N];int dis[N],rpath[N],sta[N];void build(int s,int e,int cap){    arc[num].to = e;    arc[num].c = cap;    arc[num].next = head[s];    head[s] = num ++;    arc[num - 1].pre = num;    arc[num].pre = num - 1;    arc[num].to = s;    arc[num].c = 0;    arc[num].next = head[e];    head[e] = num ++;}void re_Bfs(){    int i,front,rear;    for(i = 0;i <= n + 1;i ++)    {        cnt[i] = 0;        dis[i] = inf;    }    front = rear = 0;    que[rear ++] = n + 1;    dis[n + 1] = 0;    cnt[0] = 1;    while(front != rear)    {        int u = que[front ++];        for(i = head[u];i != -1;i = arc[i].next)        {            if(arc[arc[i].pre].c == 0 || dis[arc[i].to] < inf)                continue;            dis[arc[i].to] = dis[u] + 1;            cnt[dis[arc[i].to]] ++;            que[rear ++] = arc[i].to;        }    }}void ISAP(){    re_Bfs();    int i,u,v;    int maxflow = 0;    for(i = 0;i <= n + 1;i ++)        sta[i] = head[i];    u = 0;    while(dis[0] < n + 2)    {        if(u == n + 1)        {            int curflow = inf;            for(i = 0;i != n + 1;i = arc[sta[i]].to)                curflow = min(curflow,arc[sta[i]].c);            for(i = 0;i != n + 1;i = arc[sta[i]].to)            {                arc[sta[i]].c -= curflow;                arc[arc[sta[i]].pre].c += curflow;            }            maxflow += curflow;            u = 0;        }        for(i = sta[u];i != -1;i = arc[i].next)            if(arc[i].c && dis[u] == dis[arc[i].to] + 1)                break;        if(i != -1)        {            sta[u] = i;            rpath[arc[i].to] = arc[i].pre;            u = arc[i].to;        }        else        {            if((--cnt[dis[u]]) == 0)                break;            sta[u] = head[u];            int Min = inf;            for(i = head[u];i != -1;i = arc[i].next)                if(arc[i].c)                    Min = min(Min,dis[arc[i].to]);            dis[u] = Min + 1;            cnt[dis[u]] ++;            if(u != 0)                u = arc[rpath[u]].to;        }    }    printf("%d\n",maxflow);}int nextint(){    char c;    int ret = 0;    while((c = getchar()) > '9' || c < '0')        ;    ret = c - '0';    while((c = getchar()) >= '0' && c <= '9')        ret = ret * 10 + c - '0';    return ret;}int main(){    int i,u,v,cap;    //freopen("data.in","r",stdin);    while(scanf("%d",&n) != EOF)    {        memset(head,-1,sizeof(head));        num = 0;        np = nextint();nc = nextint();m = nextint();        //scanf("%d%d%d",&np,&nc,&m);        while(m --)        {            u = nextint();v = nextint();cap = nextint();            build(u + 1,v + 1,cap);        }        while(np --)        {            u = nextint();cap = nextint();            build(0,u + 1,cap);        }        while(nc --)        {            u = nextint();cap = nextint();            build(u + 1,n + 1,cap);        }        ISAP();    }    return 0;}//1008K16MS