題目鏈接 P2472 [SCOI2007]蜥蜴
期間一直沒有過樣例,後來想了想,是我的這裏需要考慮謹慎:
這裏很重要,可千萬別寫成了BFS搜索時候的去往臨近點的形式了。
然後剩下的就是最大流了,簡單的拆點,然後構圖,這裏就不深入講了。
對了,題目所說的距離,值得是歐幾里得距離。
#include <iostream>
#include <cstdio>
#include <cmath>
#include <string>
#include <cstring>
#include <algorithm>
#include <limits>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <bitset>
#include <unordered_map>
#include <unordered_set>
#define lowbit(x) ( x&(-x) )
#define pi 3.141592653589793
#define e 2.718281828459045
#define INF 0x3f3f3f3f3f3f3f3f
#define eps 1e-8
#define HalF (l + r)>>1
#define lsn rt<<1
#define rsn rt<<1|1
#define Lson lsn, l, mid
#define Rson rsn, mid+1, r
#define QL Lson, ql, qr
#define QR Rson, ql, qr
#define myself rt, l, r
#define MP(a, b) make_pair(a, b)
using namespace std;
typedef unsigned long long ull;
typedef unsigned int uit;
typedef long long ll;
const int dir[4][2] =
{
1, 1,
1, -1,
-1, 1,
-1, -1
};
const int maxN = 1e3 + 7, maxM = 5e4 + 7;
int N, M, D, S, T, head[maxN], cnt, cur[maxN];
struct Eddge
{
int nex, to; ll flow;
Eddge(int a=-1, int b=0, ll c=0):nex(a), to(b), flow(c) {}
}edge[maxM];
inline void addEddge(int u, int v, ll w)
{
edge[cnt] = Eddge(head[u], v, w);
head[u] = cnt++;
}
inline void _add(int u, int v, ll w) { addEddge(u, v, w); addEddge(v, u, 0); }
struct Max_Flow
{
int gap[maxN], d[maxN], que[maxN], ql, qr, node;
inline void init()
{
for(int i=0; i<=node + 1; i++)
{
gap[i] = d[i] = 0;
cur[i] = head[i];
}
++gap[d[T] = 1];
que[ql = qr = 1] = T;
while(ql <= qr)
{
int x = que[ql ++];
for(int i=head[x], v; ~i; i=edge[i].nex)
{
v = edge[i].to;
if(!d[v]) { ++gap[d[v] = d[x] + 1]; que[++qr] = v; }
}
}
}
inline ll aug(int x, ll FLOW)
{
if(x == T) return FLOW;
int flow = 0;
for(int &i=cur[x], v; ~i; i=edge[i].nex)
{
v = edge[i].to;
if(d[x] == d[v] + 1)
{
ll tmp = aug(v, min(FLOW, edge[i].flow));
flow += tmp; FLOW -= tmp; edge[i].flow -= tmp; edge[i ^ 1].flow += tmp;
if(!FLOW) return flow;
}
}
if(!(--gap[d[x]])) d[S] = node + 1;
++gap[++d[x]]; cur[x] = head[x];
return flow;
}
inline ll max_flow()
{
init();
ll ret = aug(S, INF);
while(d[S] <= node) ret += aug(S, INF);
return ret;
}
} mf;
inline int _ID(int x, int y) { return x * M + y; }
inline bool In_Map(int x, int y) { return x >= 0 && y >= 0 && x < N && y < M; }
char mp[25];
inline void init()
{
cnt = 0; S = 2 * N * M; T = S + 1; mf.node = T + 1;
for(int i=0; i<=mf.node; i++) head[i] = -1;
}
int main()
{
scanf("%d%d%d", &N, &M, &D);
init();
for(int i=0, val, xx, yy; i<N; i++)
{
scanf("%s", mp);
for(int j=0; j<M; j++)
{
val = mp[j] - '0';
if(val) _add(_ID(i, j), N * M + _ID(i, j), val);
for(int dx=0; dx<=D; dx++)
{
for(int dy=0; dy<=D; dy++)
{
if(!dx && !dy) continue;
if(dx * dx + dy * dy > D * D) continue;
for(int k=0; k<4; k++)
{
xx = i + dx * dir[k][0]; yy = j + dy * dir[k][1];
if(xx == i && yy == j) continue;
if(!In_Map(xx, yy)) _add(N * M + _ID(i, j), T, INF);
else _add(N * M + _ID(i, j), _ID(xx, yy), INF);
}
}
}
}
}
ll sum = 0;
for(int i=0; i<N; i++)
{
scanf("%s", mp);
for(int j=0; j<M; j++)
{
if(mp[j] == 'L')
{
_add(S, _ID(i, j), 1);
sum ++;
}
}
}
printf("%lld\n", sum - mf.max_flow());
return 0;
}