USACO 4.2.1 Drainage Ditches 草地排水 ditch
很明显的网络最大流问题,我用的是Edmonds-Karp算法实现的。 Edmonds-Karp 算法步骤
每次通过BFS,找到残余网络上从源点到汇点的一条最短增广路
在流网络上增加增广路
修改残余网络,残余容量减去增广路,并添加增广路的反向弧
当无法BFS到增广路时,算法结束
USER: CmYkRgB CmYkRgB [cmykrgb1] TASK: ditch LANG: C++ Compiling... Compile: OK Executing... Test 1: TEST OK [0.000 secs, 3160 KB] Test 2: TEST OK [0.000 secs, 3156 KB] Test 3: TEST OK [0.000 secs, 3156 KB] Test 4: TEST OK [0.011 secs, 3160 KB] Test 5: TEST OK [0.000 secs, 3160 KB] Test 6: TEST OK [0.022 secs, 3156 KB] Test 7: TEST OK [0.000 secs, 3156 KB] Test 8: TEST OK [0.000 secs, 3160 KB] Test 9: TEST OK [0.011 secs, 3160 KB] Test 10: TEST OK [0.000 secs, 3160 KB] Test 11: TEST OK [0.011 secs, 3156 KB] Test 12: TEST OK [0.000 secs, 3160 KB] All tests OK. YOUR PROGRAM ('ditch') WORKED FIRST TIME! That's fantastic -- and a rare thing. Please accept these special automated congratulations.
/*
ID: cmykrgb1
PROG: ditch
LANG: C++
*/
#include <iostream>
#include <fstream>
#define MAX 201
using namespace std;
class Tadjl
{
public:
class Tnode
{
public:
int r,v;
void set(int tr,int tv)
{
r=tr;
v=tv;
}
};
int cnt;
Tnode link[MAX];
};
class tQueue
{
public:
class linklist
{
public:
linklist* next;
int value;
linklist()
{
next=0;
value=0;
}
};
linklist *first,*last;
int size;
void add(int p)
{
if (size==0)
first=last=new linklist;
else
last=last->next=new linklist;
last->value=p;
size++;
}
int del()
{
int rtn=first->value;
linklist *tfirst=first;
first=first->next;
delete tfirst;
size--;
return rtn;
}
void reset()
{
size=0;
first=last=0;
}
tQueue()
{
reset();
}
};
ifstream fi("ditch.in");
ofstream fo("ditch.out");
Tadjl adjl[MAX];
int N,M,ans;
inline int min(int a,int b)
{
return a<b?a:b;
}
void init()
{
int i,a,b,v;
fi >> N >> M;
for (i=1;i<=N;i++)
{
fi >> a >> b >> v;
adjl[a].link[ ++adjl[a].cnt].set(b,v);
}
}
int edmonds(int start,int end)
{
int i,j,k;
int father[MAX],fp[MAX],max[MAX];
int Maxflow=0;
memset(father,0,sizeof(father));
max[start]=0x7FFFFFFF;
tQueue *Q=new tQueue;
Q->add(start);
while (Q->size)
{
i=Q->del();
for (k=1;k<=adjl[i].cnt;k++)
{
j=adjl[i].link[k].r;
if (!adjl[i].link[k].v || j==start) continue;
if (!father[j])
{
father[j]=i;
fp[j]=k;
max[j]=min(adjl[i].link[k].v,max[i]);
if (j==end)
{
Maxflow+=max[j];
while (father[j])
{
adjl[father[j]].link[fp[j]].v-=max[end];
adjl[j].link[++adjl[j].cnt].set(father[j],max[j]);
j=father[j];
}
memset(father,0,sizeof(father));
Q->reset();
Q->add(start);
break;
}
Q->add(j);
}
}
}
return Maxflow;
}
void print()
{
fo << ans << endl;
fi.close();
fo.close();
}
int main()
{
init();
ans=edmonds(1,M);
print();
return 0;
}
上次修改时间 2017-05-22