bzoj 1001
[BeiJing2006]狼抓兔子
题解
平面图的最大流转换为最短路问题， 详见周东的《两极相通》.
示例代码
#include <cstdio>
#include <deque>
#include <bitset>
#include <cstring>
#include <cassert>
using namespace std;
typedef long long int ll;
#define MAXV 2000200
#define MAXE 6000600
struct edge
{
int v;
ll w;
edge *n;
edge(int vv = 0, ll ww = 0ll, edge *nn = NULL) : v(vv), w(ww), n(nn) { }
}E[MAXE];
int ne;
edge *front[MAXV];
void add_edge(int u, int v, ll w)
{
E[ne] = edge(v, w, u[front]);
u[front] = E + ne;
ne ++;
}
ll d[MAXV];
bitset<MAXV> inq;
ll sp(int s, int t)
{
deque<int> q;
memset(d, 0x7f, sizeof d);
q.push_back(s);
d[s] = 0;
inq.set(s);
while ( !q.empty() )
{
int u = q.front();
q.pop_front(); inq.reset(u);
for (edge *e = u[front]; e; e = e->n)
{
int v = e->v; ll w = e->w;
if ( d[v] > d[u] + w )
{
d[v] = d[u] + w;
if ( !inq.test(v) )
{
if ( d[v] < d[q.front()] )
q.push_front(v);
else
q.push_back(v);
inq.set(v);
}
}
}
}
return d[t];
}
#define s (0)
#define t (MAXV-1)
#define lb(x) (2*(x) - 1)
#define ru(x) (2*(x))
int main(void)
{
int N, M;
ll w;
scanf("%d%d", &N, &M);
assert(N > 1 || M > 1);
/* - */
/* first line */
for (int i = 1; i < M; i++)
{
scanf("%lld", &w);
if (1 == N)
{
add_edge(s, t, w);
add_edge(t, s, w);
} else {
add_edge(s, ru(i), w);
add_edge(ru(i), s, w);
}
}
for (int i = 1; i < N - 1; i++)
{
int up = 1 + (i - 1) * (M - 1);
int down = up + M - 1;
for (int j = 1; j < M; j++)
{
scanf("%lld", &w);
add_edge(lb(up), ru(down), w);
add_edge(ru(down), lb(up), w);
up ++; down ++;
}
}
/* last line */
if (N > 1)
{
int block = 1 + (N - 2) * (M - 1);
for (int i = 1; i < M; i++)
{
scanf("%lld", &w);
add_edge(lb(block), t, w);
add_edge(t, lb(block), w);
block ++;
}
}
/* | */
for (int i = 1; i < N; i++)
{
if (1 == M)
{
scanf("%lld", &w);
add_edge(s, t, w);
add_edge(t, s, w);
} else {
int block = 1 + (i - 1) * (M - 1);
scanf("%lld", &w);
add_edge(t, lb(block), w); add_edge(lb(block), t, w);
for (int j = 1; j < M - 1; j++)
{
scanf("%lld", &w);
add_edge(ru(block), lb(block + 1), w);
add_edge(lb(block + 1), ru(block), w);
block ++;
}
scanf("%lld", &w);
add_edge(ru(block), s, w);
add_edge(s, ru(block), w);
}
}
/* \ */
for (int i = 1; i < N; i++)
{
int blk = 1 + (i - 1) * (M - 1);
for (int j = 1; j < M; j++)
{
scanf("%lld", &w);
add_edge(lb(blk), ru(blk), w);
add_edge(ru(blk), lb(blk), w);
blk ++;
}
}
/* --- */
printf("%lld\n", sp(s, t));
return 0;
}
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