[codevs 1914] 运输问题

[codevs 1914] 运输问题

题解：

直接看要求建图，求费用流取相反数输出，再改边费用求费用流输出。

代码：

总时间耗费: 58ms 
总内存耗费: 364B

#include<cstdio>
#include<iostream>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;

const int maxn = 500 + 10;
const int INF = 1e9 + 7;

struct Edge {
	int from, to, cap, flow, cost;
};

int s, t;
vector<int> G[maxn];
vector<Edge> edges;

void AddEdge(int from, int to, int cap, int cost) {
	edges.push_back((Edge){from, to, cap, 0, cost});
	edges.push_back((Edge){to, from, 0, 0, -cost});
	int m = edges.size();
	G[from].push_back(m-2);
	G[to].push_back(m-1);
}

int d[maxn], p[maxn], a[maxn];
bool inq[maxn];

bool BellmanFord(int& cost) {
	memset(inq, 0, sizeof(inq));
	for(int i = s; i <= t; i++) d[i] = INF;
	d[s] = 0; inq[s] = 1; p[s] = 0; a[s] = INF;
	
	queue<int> Q;
	Q.push(s);
	while(!Q.empty()) {
		int x = Q.front(); Q.pop();
		inq[x] = 0;
		for(int i = 0; i < G[x].size(); i++) {
			Edge& e = edges[G[x][i]];
			if(e.cap > e.flow && d[e.to] > d[x] + e.cost) {
				d[e.to] = d[x] + e.cost;
				a[e.to] = min(a[x], e.cap-e.flow);
				p[e.to] = G[x][i];
				if(!inq[e.to]) { Q.push(e.to); inq[e.to] = 1; }
			}
		}
	}
	if(d[t] == INF) return 0;
	
	cost += d[t]*a[t];
	int x = t;
	while(x != s) {
		edges[p[x]].flow += a[t];
		edges[p[x]^1].flow -= a[t];
		x = edges[p[x]].from;
	}
	
	return 1;
}

int MincostMaxflow() {
	int cost = 0;
	while(BellmanFord(cost));
	return cost;
}
	
int main() {
	int m, n;
	cin >> m >> n;
	s = 0; t = m + n + 1;
	
	for(int i = 1; i <= m; i++) {
		int cap; cin >> cap;
		AddEdge(s, i, cap, 0);
	}
	
	for(int i = m+1; i <= m+n; i++) {
		int cap; cin >> cap;
		AddEdge(i, t, cap, 0);
	}
	
	for(int i = 1; i <= m; i++)
		for(int j = m+1; j <= m+n; j++) {
			int cost; cin >> cost;
			AddEdge(i, j, INF, cost);
		}
		
	cout << MincostMaxflow() << endl;
	
	for(int i = 0; i < edges.size(); i++) {
		Edge& e = edges[i];
		e.flow = 0; e.cost = -e.cost;
	}
	
	cout << -MincostMaxflow() << endl;
	return 0;
}