费用流 poj2195 Going Home

传送门：点击打开链接

费用流裸题，，感觉不是因为我模板慢，，应该是因为vector的原因。。

题意：每个人都要回已房子，费用是哈曼顿距离，每个房子只能容纳1人，问最小费用

超级源点连接每一个人，每个人再连很多条边对应房子

再把每个房子连接超级汇点

模板一套，，就做完了

#include<map>
#include<set>
#include<cmath>
#include<stack>
#include<queue>
#include<cstdio>
#include<string>
#include<vector>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<functional>

using namespace std;
typedef long long LL;
typedef pair<int, int> PII;

const int MX = 80000 + 5;//都开4倍把..
const int MM = 80000 + 5;
const int INF = 0x3f3f3f3f;

struct Edge {
int to, next, cap, flow, cost;
Edge() {}
Edge(int _to, int _next, int _cap, int _flow, int _cost) {
to = _to; next = _next; cap = _cap; flow = _flow; cost = _cost;
}
} E[MM];

int Head[MX], tol;
int pre[MX]; //储存前驱顶点
int dis[MX]; //储存到源点s的距离
bool vis[MX];
int N;//节点总个数，节点编号从0~N-1

void init(int n) {
tol = 0;
N = 2 * n + 2;
memset(Head, -1, sizeof(Head));
}
void addedge(int u, int v, int cap, int cost) {
E[tol] = Edge(v, Head[u], cap, 0, cost);
Head[u] = tol++;

E[tol] = Edge(u, Head[v], 0, 0, -cost);
Head[v] = tol++;
}
bool spfa(int s, int t) {
queue<int>q;
for (int i = 0; i < N; i++) {
dis[i] = INF;
vis[i] = false;
pre[i] = -1;
}
dis[s] = 0;
vis[s] = true;
q.push(s);
while (!q.empty()) {
int u = q.front();
q.pop();
vis[u] = false;
for (int i = Head[u]; i != -1; i = E[i].next) {
int v = E[i].to;
if (E[i].cap > E[i].flow && dis[v] > dis[u] + E[i].cost) {
dis[v] = dis[u] + E[i].cost;
pre[v] = i;
if (!vis[v]) {
vis[v] = true;
q.push(v);
}
}
}
}
if (pre[t] == -1) return false;
else return true;
}

//返回的是最大流， cost存的是最小费用
int minCostMaxflow(int s, int t, int &cost) {
int flow = 0;
cost = 0;
while (spfa(s, t)) {
int Min = INF;
for (int i = pre[t]; i != -1; i = pre[E[i ^ 1].to]) {
if (Min > E[i].cap - E[i].flow)
Min = E[i].cap - E[i].flow;
}
for (int i = pre[t]; i != -1; i = pre[E[i ^ 1].to]) {
E[i].flow += Min;
E[i ^ 1].flow -= Min;
cost += E[i].cost * Min;
}
flow += Min;
}
return flow;
}

int m, n;
char S[1000];
vector<PII>Beg, End;

int dist(PII a, PII b) {
return abs(a.first - b.first) + abs(a.second - b.second);
}

int main() {
//freopen("input.txt", "r", stdin);
while(~scanf("%d%d", &m, &n), m + n) {
Beg.clear();
End.clear();

for(int i = 0; i < m; i++) {
scanf("%s", S);
for(int j = 0; j < n; j++) {
if(S[j] == 'm') Beg.push_back(PII(i, j));
if(S[j] == 'H') End.push_back(PII(i, j));
}
}

init(Beg.size() + End.size());
int s = 0, t = 2 * (Beg.size() + End.size()) + 1;

for(int i = 0; i < Beg.size(); i++) {
addedge(s, i + 1, 1, 0);
}

for(int i = 0; i < End.size(); i++) {
addedge(i + Beg.size() + 1, t, 1, 0);
}

for(int i = 0; i < Beg.size(); i++) {
for(int j = 0; j < End.size(); j++) {
addedge(i + 1, Beg.size() + j + 1, 1, dist(Beg[i], End[j]));
}
}

int ans = 0;
minCostMaxflow(s, t, ans);
printf("%d\n", ans);
}
return 0;
}