POJ2195 Going Home

嘟嘟嘟


费用流水题。


从源点向每一个人连一条容量为1，费用为0的边；从每一个人向每一栋房子连一条容量为1，费用为两点欧几里得距离的边；从每一栋房子向汇点连一条容量为1，费用为0的边。
跑最小费用最大流即可。


祭写\(spfa\)时又忘了弹栈后把标记数组清空。

#include<cstdio>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<cstdlib>
#include<cctype>
#include<vector>
#include<stack>
#include<queue>
using namespace std;
#define enter puts("") 
#define space putchar(' ')
#define Mem(a, x) memset(a, x, sizeof(a))
#define rg register
typedef long long ll;
typedef double db;
const int INF = 0x3f3f3f3f;
const db eps = 1e-8;
const int maxn = 105;
const int maxe = 5e6 + 5;
inline ll read()
{
  ll ans = 0;
  char ch = getchar(), last = ' ';
  while(!isdigit(ch)) last = ch, ch = getchar();
  while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar();
  if(last == '-') ans = -ans;
  return ans;
}
inline void write(ll x)
{
  if(x < 0) x = -x, putchar('-');
  if(x >= 10) write(x / 10);
  putchar(x % 10 + '0');
}

int n, m, s, t;
char a[maxn][maxn];
struct Edge
{
  int nxt, from, to, cap, c;
}e[maxe];
int head[maxn * maxn], ecnt = -1;
void addEdge(int x, int y, int w, int c)
{
  e[++ecnt] = (Edge){head[x], x, y, w, c};
  head[x] = ecnt;
  e[++ecnt] = (Edge){head[y], y, x, 0, -c};
  head[y] = ecnt;
}

int num(int i, int j)
{
  return (i - 1) * m + j;
}
struct Node
{
  int x, y;
}h[maxn * maxn];
int cnt = 0;
void build(int x, int y)
{
  addEdge(s, num(x, y), 1, 0);
  for(int i = 1; i <= cnt; ++i)
    addEdge(num(x, y), num(h[i].x, h[i].y), 1, abs(x - h[i].x) + abs(y - h[i].y));
}

bool in[maxn * maxn];
int dis[maxn * maxn], pre[maxn * maxn], flow[maxn * maxn];
bool spfa()
{
  Mem(in, 0); Mem(dis, 0x3f);
  queue<int> q; q.push(s);
  in[s] = 1; dis[s] = 0; flow[s] = INF;
  while(!q.empty())
    {
      int now = q.front(); q.pop(); in[now] = 0;
      for(int i = head[now], v; i != -1; i = e[i].nxt)
	{
	  v = e[i].to;
	  if(e[i].cap && dis[now] + e[i].c < dis[v])
	    {
	      dis[v] = dis[now] + e[i].c;
	      pre[v] = i;
	      flow[v] = min(flow[now], e[i].cap);
	      if(!in[v]) in[v] = 1, q.push(v);
	    }
	}
    }
  return dis[t] != INF;
}
int minCost = 0;
void update()
{
  int x = t;
  while(x != s)
    {
      int i = pre[x];
      e[i].cap -= flow[t];
      e[i ^ 1].cap += flow[t];
      x = e[i].from;
    }
  minCost += flow[t] * dis[t];
}
void MCMF()
{
  while(spfa()) update(); 
}

void init()
{
  Mem(head, -1); ecnt = -1;
  minCost = 0;
}

int main()
{
  while(scanf("%d%d", &n, &m) != EOF && n && m)
    {
      init();
      s = 0; t = n * m + 1;
      for(int i = 1; i <= n; ++i) scanf("%s", a[i] + 1);
      for(int i = 1; i <= n; ++i)
	for(int j = 1; j <= m; ++j)
	  if(a[i][j] == 'H') addEdge(num(i, j), t, 1, 0), h[++cnt] = (Node){i, j};
      for(int i = 1; i <= n; ++i)
	for(int j = 1; j <= m; ++j)
	  if(a[i][j] == 'm') build(i, j);
      MCMF();
      write(minCost), enter;
    }
  return 0;
}