[SCOI2007]蜥蜴【最大流模板】

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;
}

 

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