Luogu P1251 餐巾计划问题

题目链接 (Click) (Here)

看到其他人都是用费用流写的，我只能表示：动什么脑子？暴力就完事了！

嗯，这个题应该是一个相当显然的上下界最小费用可行流模型，所以跑就完事了。

(s -> inn (i)) (f = INF) (w = buy) 新买

(out (i) -> inn (i + fast)) (f = INF) (w = fastw) 快洗

(out(i) ->inn(i + slow)) (f = INF) (w = sloww) 慢洗

(out(i) -> T) 不洗

(inn(i)->out(i)) (f = [use[i],use[i]]) (w=0) 不洗

还有一个小小的坑了我一下。

(inn (i) -> inn (i + 1)) (f=INF) (w=0) 洗完不用留着

就是这样，然后套路最小费用可行流即可。

#include <bits/stdc++.h>
#define int long long
#define INF 0x3f3f3f3f3f3f3f3f
#define N 4010
#define M 4000010
using namespace std;

struct Graph {
    int cnt, head[N];
    
    struct edge {
        int nxt, to, f, w;
    }e[M];
    
    void add_edge (int from, int to, int flw, int val) {
        e[++cnt].nxt = head[from];
        e[cnt].to = to;
        e[cnt].f = flw;
        e[cnt].w = val;
        head[from] = cnt;
    }
    
    Graph () {
        cnt = -1;
        memset (head, -1, sizeof (head));
    }
}G1;

namespace _EK {
    int vis[N], dis[N], flow[N];
    int pre_edge[N], pre_node[N];
    
    queue <int> q;
    #define fpop(x) x.front();x.pop()
    
    bool spfa (int s, int t, Graph &G) {
        memset (vis, 0, sizeof (vis));
        memset (dis, 0x3f, sizeof (dis));
        memset (flow, 0x3f, sizeof (flow));
        vis[s] = true, dis[s] = 0; q.push (s);
        while (!q.empty ()) {
            int u = fpop (q);
            for (int i = G.head[u]; ~i; i = G.e[i].nxt) {
                int v = G.e[i].to;
                if (dis[v] > dis[u] + G.e[i].w && G.e[i].f) {
                    dis[v] = dis[u] + G.e[i].w;
                    flow[v] = min (flow[u], G.e[i].f);
                    pre_edge[v] = i;
                    pre_node[v] = u;
                    if (!vis[v]) {
                        vis[v] = true;
                        q.push (v);
                    }
                }
            }
            vis[u] = false;
        }
        return dis[t] != INF;
    }	
}

int EK (int s, int t, Graph &G) {
    int max_flow = 0, min_cost = 0;
    while (_EK :: spfa (s, t, G)) {
        max_flow += _EK :: flow[t];
        min_cost += _EK :: flow[t] * _EK :: dis[t];
        int u = t;
        while (u != s) {
            G.e[_EK :: pre_edge[u] ^ 0].f -= _EK :: flow[t];
            G.e[_EK :: pre_edge[u] ^ 1].f += _EK :: flow[t];
            u = _EK :: pre_node[u];
        }	
    }
	return min_cost;
}

void add_len (int u, int v, int f, int w) {
	G1.add_edge (u, v, f, +w);
	G1.add_edge (v, u, 0, -w);
}

int n, bw, qt, st, qw, sw, use[N], flow[N];

int inn (int x) {return n * 0 + x;}
int out (int x) {return n * 1 + x;}

signed main () {
	freopen ("data.in", "r", stdin);
	cin >> n;
	int s = n * 2 + 1, t = n * 2 + 2;
	int ss = n * 2 + 3, tt = n * 2 + 4;
	for (int i = 1; i <= n; ++i) cin >> use[i];
	cin >> bw >> qt >> qw >> st >> sw;
	for (int i = 1; i <= n; ++i) {
		add_len (s, inn (i), INF, bw);
		add_len (out (i), t, INF, 00);
		if (i + qt <= n) add_len (out (i), inn (i + qt), INF, qw);
		if (i + st <= n) add_len (out (i), inn (i + st), INF, sw);
		flow[out (i)] += use[i];
		flow[inn (i)] -= use[i];
	}
	for (int i = 1; i < n; ++i) {
		add_len (inn (i), inn (i + 1), INF, 0);
	}
	for (int i = inn (1); i <= out (n); ++i) {
		if (flow[i] > 0) add_len (ss, i, +flow[i], 0);
		if (flow[i] < 0) add_len (i, tt, -flow[i], 0);
	}
	add_len (t, s, INF, 0);
	cout << EK (ss, tt, G1) << endl;
}