HDU 3452 Bonsai(网络流之最小割）

来源：互联网发布：mac下制作win7安装u盘编辑：程序博客网时间：2024/05/20 05:25

题目地址：HDU 3452

最小割水题。源点为根节点，再另设一汇点，汇点与叶子连边。对叶子结点的判断是看度数是否为1.

代码如下：

#include <iostream>#include <cstdio>#include <string>#include <cstring>#include <stdlib.h>#include <math.h>#include <ctype.h>#include <queue>#include <map>#include <set>#include <algorithm>using namespace std;const int INF=0x3f3f3f3f;int head[3000], source, sink, nv, cnt, deg[2000];int cur[3000], num[3000], d[3000], pre[3000];struct node{    int u, v, cap, next;} edge[1000000];void add(int u, int v, int cap){    edge[cnt].v=v;    edge[cnt].cap=cap;    edge[cnt].next=head[u];    head[u]=cnt++;    edge[cnt].v=u;    edge[cnt].cap=0;    edge[cnt].next=head[v];    head[v]=cnt++;}void bfs(){    memset(num,0,sizeof(num));    memset(d,-1,sizeof(d));    queue<int>q;    q.push(sink);    d[sink]=0;    num[0]=1;    while(!q.empty())    {        int u=q.front();        q.pop();        for(int i=head[u]; i!=-1; i=edge[i].next)        {            int v=edge[i].v;            if(d[v]==-1)            {                d[v]=d[u]+1;                num[d[v]]++;                q.push(v);            }        }    }}int isap(){    memcpy(cur,head,sizeof(cur));    int flow=0, u=pre[source]=source, i;    bfs();    while(d[source]<nv)    {        if(u==sink)        {            int f=INF, pos;            for(i=source; i!=sink; i=edge[cur[i]].v)            {                if(f>edge[cur[i]].cap)                {                    f=edge[cur[i]].cap;                    pos=i;                }            }            for(i=source; i!=sink; i=edge[cur[i]].v)            {                edge[cur[i]].cap-=f;                edge[cur[i]^1].cap+=f;            }            flow+=f;            u=pos;        }        for(i=cur[u]; i!=-1; i=edge[i].next)        {            if(d[edge[i].v]+1==d[u]&&edge[i].cap)                break;        }        if(i!=-1)        {            cur[u]=i;            pre[edge[i].v]=u;            u=edge[i].v;        }        else        {            if(--num[d[u]]==0) break;            int mind=nv;            for(i=head[u]; i!=-1; i=edge[i].next)            {                if(mind>d[edge[i].v]&&edge[i].cap)                {                    mind=d[edge[i].v];                    cur[u]=i;                }            }            d[u]=mind+1;            num[d[u]]++;            u=pre[u];        }    }    return flow;}int main(){    int n, i, u, v, w;    while(scanf("%d%d",&n,&source)!=EOF&&n&&source)    {        memset(head,-1,sizeof(head));        memset(deg,0,sizeof(deg));        cnt=0;        sink=n+1;        nv=sink+1;        for(i=1;i<n;i++)        {            scanf("%d%d%d",&u,&v,&w);            add(u,v,w);            add(v,u,w);            deg[u]++;            deg[v]++;        }        for(i=1;i<=n;i++)        {            if(i!=source&°[i]==1)            {                add(i,sink,INF);            }        }        printf("%d\n",isap());    }    return 0;}

0 0