OJ-Problems-Source/HDOJ/3036_autoAC.cpp
2016-08-30 22:34:56 +08:00

159 lines
4.8 KiB
C++

#include<stdio.h>
#include<string.h>
#include<iostream>
#include<algorithm>
#include<queue>
#include<vector>
using namespace std;
#define ll int
#define N 20050
#define M 105000
#define inf 10737418
struct Edge{
ll from, to, cap, nex;
}edge[M*4];
ll head[N], edgenum;
void add(ll u, ll v, ll cap){
Edge E = { u, v, cap, head[u]};
edge[ edgenum ] = E;
head[u] = edgenum ++;
Edge E2= { v, u, 0, head[v]};
edge[ edgenum ] = E2;
head[v] = edgenum ++;
}
ll sign[N];
bool BFS(ll from, ll to){
memset(sign, -1, sizeof(sign));
sign[from] = 0;
queue<ll>q;
q.push(from);
while( !q.empty() ){
int u = q.front(); q.pop();
for(ll i = head[u]; i!=-1; i = edge[i].nex)
{
ll v = edge[i].to;
if(sign[v]==-1 && edge[i].cap)
{
sign[v] = sign[u] + 1, q.push(v);
if(sign[to] != -1)return true;
}
}
}
return false;
}
ll Stack[N], top, cur[N];
ll dinic(ll from, ll to){
ll ans = 0;
while( BFS(from, to) )
{
memcpy(cur, head, sizeof(head));
ll u = from; top = 0;
while(1)
{
if(u == to)
{
ll flow = inf, loc;
for(ll i = 0; i < top; i++)
if(flow > edge[ Stack[i] ].cap)
{
flow = edge[Stack[i]].cap;
loc = i;
}
for(ll i = 0; i < top; i++)
{
edge[ Stack[i] ].cap -= flow;
edge[Stack[i]^1].cap += flow;
}
ans += flow;
top = loc;
u = edge[Stack[top]].from;
}
for(ll i = cur[u]; i!=-1; cur[u] = i = edge[i].nex)
if(edge[i].cap && (sign[u] + 1 == sign[ edge[i].to ]))break;
if(cur[u] != -1)
{
Stack[top++] = cur[u];
u = edge[ cur[u] ].to;
}
else
{
if( top == 0 )break;
sign[u] = -1;
u = edge[ Stack[--top] ].from;
}
}
}
return ans;
}
void init(){memset(head,-1,sizeof head);edgenum = 0;}
char mp[15][15];
int n, m, T;
int Hash(int x,int y){return x*m+y;}
vector<int>E,P;
int dis[150][150], step[4][2]={1,0,-1,0,0,1,0,-1};
bool vis[150][150];
void bfs(int sx,int sy){
int start = Hash(sx,sy);
memset(vis, 0, sizeof vis);
vis[sx][sy] = 1;
dis[start][start] = 0;
queue<int>qx,qy; while(!qx.empty())qx.pop(); while(!qy.empty())qy.pop();
qx.push(sx), qy.push(sy);
while(!qx.empty()){
int x = qx.front(), y = qy.front();
qx.pop(); qy.pop();
for(int i = 0; i < 4; i++){
int dx = x + step[i][0], dy = y + step[i][1];
if(!(0<=dx&&dx<n&&0<=dy&&dy<m))continue;
if(vis[dx][dy] || mp[dx][dy]!='.')continue;
vis[dx][dy] = 1;
dis[Hash(dx,dy)][start] = dis[start][Hash(dx,dy)] = dis[start][Hash(x,y)]+1;
qx.push(dx); qy.push(dy);
}
}
}
bool ok(int TIME){
init();
int from = N-2, to = N-1;
for(int i = 0; i < P.size(); i++)add(from, P[i], 1);
for(int i = 0; i < P.size(); i++)
{
for(int j = 0; j < E.size(); j++)
if(dis[P[i]][E[j]]<=TIME) add(P[i],j*150+150+dis[P[i]][E[j]],1);
}
for(int i = 0; i < E.size(); i++)
for(int j = 1; j <= TIME; j++)
{
add(i*150+150+j, to, 1);
if(j!=TIME)
add(i*150+150+j,i*150+150+j+1,inf);
}
return dinic(from,to)==P.size();
}
int main(){
int i, j;
while(~scanf("%d %d %d",&n,&m,&T)){
E.clear(); P.clear();
memset(dis, 0, sizeof dis);
memset(mp, 0, sizeof mp);
for(i=0;i<n;i++)scanf("%s",mp[i]);
for(i=0;i<n;i++)for(j=0;j<m;j++)
{
if(mp[i][j]=='E')E.push_back(Hash(i,j));
else if(mp[i][j]=='.')P.push_back(Hash(i,j));
}
if(P.size()==0){puts("0");continue;} if(E.size()==0){puts("impossible");continue;}
for(i = 0; i < E.size(); i++)bfs(E[i]/m, E[i]%m);
int l = 1, r = 256, ans = inf;
while(l<=r)
{
int mid = (l+r)>>1;
if(ok(mid))ans = min(ans, mid), r = mid-1;
else l = mid+1;
}
if(T<ans || ans==inf){puts("impossible");continue;}
else printf("%d\n",ans);
}
return 0;
}