AOJ 2290: Attack the Moles

ブログに記事を書きます Advent Calendar 2014 - Adventar7日目。


最小費用流はBellman-Fordを1回やって流量くらいの回数Dijkstraをするらしい。
また、Bellman-Fordはうまくトポロジカル順に行うとよい。

と、最小費用流に関する理解を深めた(といいたいが、いまだに仕組みをわかっていない)

#include<stdio.h>
#include<string.h>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;
namespace MCF {
	// required <string.h> <vector> <queue> <algorithm>
	#define MAXN 6100
	#define MAXM 21000000
	#define wint int
	#define cint int
	const wint wEPS = 0;
	const wint wINF = 1001001001;
	const cint cEPS = 0;
	const cint cINF = 1001001001;
	int n, m, ptr[MAXN], next[MAXM], zu[MAXM];
	wint capa[MAXM], tof;
	cint cost[MAXM], toc, d[MAXN], pot[MAXN];
	int vis[MAXN], pree[MAXN];
	void init(int _n) {
		n = _n; m = 0; memset(ptr, ~0, n * 4);
	}
	void ae(int u, int v, wint w, cint c) {
		next[m] = ptr[u]; ptr[u] = m; zu[m] = v; capa[m] = w; cost[m] = +c; ++m;
		next[m] = ptr[v]; ptr[v] = m; zu[m] = u; capa[m] = 0; cost[m] = -c; ++m;
	}
	bool solve(int src, int ink, wint flo = wINF) {
		int i, u, v;
		wint f;
		cint c, cc;
		memset(pot, 0, n * sizeof(cint));
		
		for (bool cont = 1; cont; ) {
			cont = 0;
			for (u = 0; u < n; ++u) for (i = ptr[u]; ~i; i = next[i]) if (capa[i] > wEPS) {
				if (pot[zu[i]] > pot[u] + cost[i] + cEPS) {
					pot[zu[i]] = pot[u] + cost[i]; cont = 1;
				}
			}
		}
		for (toc = 0, tof = 0; tof + wEPS < flo; ) {
			typedef pair<cint,int> node;
			priority_queue< node,vector<node>,greater<node> > q;
			for (u = 0; u < n; ++u) { d[u] = cINF; vis[u] = 0; }
			for (q.push(make_pair(d[src] = 0, src)); !q.empty(); ) {
				c = q.top().first; u = q.top().second; q.pop();
				if (vis[u]++) continue;
				for (i = ptr[u]; ~i; i = next[i]) if (capa[i] > wEPS) {
					cc = c + cost[i] + pot[u] - pot[v = zu[i]];
					if (d[v] > cc + cEPS) { q.push(make_pair(d[v] = cc, v)); pree[v] = i; }
				}
			}
			if (!vis[ink]) return 0;
			f = flo - tof;
			for (v = ink; v != src; v = zu[i ^ 1]) { i = pree[v]; f=min(f,capa[i]); }
			for (v = ink; v != src; v = zu[i ^ 1]) { i = pree[v]; capa[i] -= f; capa[i ^ 1] += f; }
			tof += f;
			toc += f * (d[ink] - pot[src] + pot[ink]);
			for (u = 0; u < n; ++u) pot[u] += d[u];
		}
		return 1;
	}
}
int x[3100];
int t[3100];
int p[3100];
pair<int,pair<int,int> > in[3100];
int ABS(int a){return max(a,-a);}
int main(){
	int a,b,c,d;
	scanf("%d%d%d%d",&a,&b,&c,&d);
	
	int s=2*a;
	int sl=2*a+1;
	int sr=2*a+2;
	int T=2*a+3;
	int U=T+1;
	int V=U+1;
	
	MCF::init(V+1);
//	MCF::ae(U,s,2,0);
//	MCF::ae(T,V,2,0);
	MCF::ae(s,T,2,0);
	MCF::ae(s,sl,1,0);
	MCF::ae(s,sr,1,0);
	int val=0;
	for(int i=0;i<a;i++){
		scanf("%d%d%d",x+i,t+i,p+i);
		in[i]=make_pair(t[i],make_pair(x[i],p[i]));
	}
	std::sort(in,in+a);
	for(int i=0;i<a;i++){
		t[i]=in[i].first;
		x[i]=in[i].second.first;
		p[i]=in[i].second.second;
	}
	for(int i=0;i<a;i++){
		if(ABS(x[i]-c)<=t[i]*b)MCF::ae(sl,2*i,1,0);
		if(ABS(x[i]-d)<=t[i]*b)MCF::ae(sr,2*i,1,0);
		MCF::ae(2*i+1,T,1,0);
/*		MCF::ae(U,i*2+1,1,0);
		MCF::ae(i*2,V,1,0);
		MCF::ae(i*2+1,i*2,1,p[i]);*/
		MCF::ae(i*2,i*2+1,1,-p[i]);
		val-=p[i];
	//	MCF::ae(2*i,2*i+1,1,-p[i]);
	}
	for(int i=0;i<a;i++){
		for(int j=0;j<a;j++){
			if(t[i]<t[j]&&(t[j]-t[i])*b>=ABS(x[i]-x[j])){
	//			printf("%d %d\n",i,j);
				MCF::ae(i*2+1,j*2,1,0);
			}
		}
	}
	MCF::solve(s,T,2+a);
	printf("%d\n",-MCF::toc);
}