poj_2195 最小费用最大流

#include<stdio.h>
#include<string.h>
#include<queue>
#include<vector>
#include<algorithm>
#include<cmath>
using namespace std;
#define INF 1 << 25
#define MAX_NODE 220
#define MAX_EDGE_NUM 40005
#define min(a, b) a<b?a:b
struct Edge{
	int to;
	int vol;
	int cost;
	int next;
};
Edge gEdges[MAX_EDGE_NUM];
int gPre[MAX_NODE];
int gPath[MAX_NODE];
int gDist[MAX_NODE];
int gHead[MAX_NODE];
int gEdgeCount;
void InsertEdge(int u, int v, int vol, int cost){
	gEdges[gEdgeCount].to = v;
	gEdges[gEdgeCount].vol = vol;
	gEdges[gEdgeCount].cost = cost;
	gEdges[gEdgeCount].next = gHead[u];
	gHead[u] = gEdgeCount++;

	gEdges[gEdgeCount].to = u;
	gEdges[gEdgeCount].vol = 0;
	gEdges[gEdgeCount].cost = -cost;
	gEdges[gEdgeCount].next = gHead[v];
	gHead[v] = gEdgeCount++;
}
//spfa算法求最短路（即增广单位费用最小的从源到汇的路径）
bool Spfa(int s, int t){
	memset(gDist, 0x7F, sizeof(gDist));
	memset(gPre, -1, sizeof(gPre));
	gDist[s] = 0;
	queue<int>Q;
	Q.push(s);
	while (!Q.empty()){
		int u = Q.front();
		Q.pop();
		for (int e = gHead[u]; e != -1; e = gEdges[e].next){
			int v = gEdges[e].to;
			if (gEdges[e].vol > 0 && gDist[v] > gDist[u] + gEdges[e].cost){
				gDist[v] = gDist[u] + gEdges[e].cost;
				gPre[v] = u;
				gPath[v] = e;
				Q.push(v);
			}
		}
	}
	return gPre[t] != -1;
}

int MinCostFlow(int s, int t){
	int cost = 0;
	int max_flow = 0;
	int u, v, e;
	while (Spfa(s, t)){
		int f = INF;
		for (u = t; u != s; u = gPre[u]){
			f = min(f, gEdges[gPath[u]].vol);
		}

		for (u = t; u != s; u = gPre[u]){
			e = gPath[u];
			gEdges[e].vol -= f;
			gEdges[e^1].vol += f;	//反向边
		}
		max_flow += f;
		cost += f*gDist[t];
	}
	return cost;
}

char gMap[105][105];
vector<pair<int, int> > gHousVec;
vector<pair<int, int> > gManVec;
//建图
void BuildGraph(){
	int n = gHousVec.size();
	// 源点0，连接到每个小人结点，流量为1，单位费用为0
	for (int u = 1; u <= n; u++){
		InsertEdge(0, u, 1, 0);
	}
	for (int i = 0; i < n; i++){
		for (int j = 0; j < n; j++){ 
			//求出小人i到房间j的最短距离
			int min_dist = abs(gManVec[i].first - gHousVec[j].first) + abs(gManVec[i].second - gHousVec[j].second);
			//建边，连接小人i和房间j
			InsertEdge(i + 1, j + n + 1, 1, min_dist);
		}
	}
	//汇点 2*n+1，连接各个房间借点到汇点，流量为1，单位费用为0
	for (int u = 1; u <= n; u++){
		InsertEdge(n + u, 2 * n + 1, 1, 0);
	}
}
int main(){
	int n, m;
	while (scanf("%d %d", &n, &m) && n && m){
		char tmp;
		gHousVec.clear();	//初始化
		gManVec.clear();
		memset(gHead, -1, sizeof(gHead)); //图的初始化
		gEdgeCount = 0;	//图的初始化

		for (int i = 1; i <= n; i++){
			getchar();
			for (int j = 1; j <= m; j++){
				scanf("%c", &tmp);
				if (tmp == ‘H‘){
					gHousVec.push_back(pair<int, int>(i, j));
				}
				else if (tmp == ‘m‘){
					gManVec.push_back(pair<int, int>(i, j));
				}
			}
		}
		BuildGraph();  //建图
		int cost = MinCostFlow(0, 2 * gHousVec.size() + 1); //求解最小费用最大流
		printf("%d\n", cost);
	}
	return 0;
}