Uva1601双向BFS

//双向BFS
#include<cstdio>
#include<cstring>
#include<cctype>
#include<queue>
#include <iostream>
using namespace std;
const int N    = 20;
const int maxn = 200;
const int dx[] = {1,0,-1,0,0};
const int dy[] = {0,-1,0,1,0};
int n,m,k;
char maze

;
int x[maxn],y[maxn],cnt,G[maxn][5],deg[maxn],id[maxn][maxn];
int s[3],t[3];
int d[maxn][maxn][maxn],bd[maxn][maxn][maxn];
int ID(int a,int b,int c)
{
return (a<<16)|(b<<8)|c;//将状态压缩成一个整数，方便储存
}
void Memset(){
memset(d,-1,sizeof(d));
memset(bd,-1,sizeof(bd));
}
bool conflict(int a, int b, int a2, int b2) {
return a2 == b2 || (a2 == b && b2 == a);//判断是否冲突
}
queue<int> q;
bool bfs()//正向BFS
{
int value;
int uu=q.front();
int aa=(uu>>16)&0xff,bb=(uu>>8)&0xff,cc=uu&0xff;
value=d[aa][bb][cc];
while(!q.empty())
{
int u=q.front();
int a=(u>>16)&0xff,b=(u>>8)&0xff,c=u&0xff;
if(d[a][b][c]!=value) return false;
if(bd[a][b][c]!=-1) return true;
for(int i=0; i<deg[a]; i++)
{
int na=G[a][i];
for(int j=0; j<deg[b]; j++)
{
int nb=G[b][j];
for(int k=0; k<deg[c]; k++)
{
int nc=G[c][k];
if(conflict(a,b,na,nb)) continue;
if(conflict(a,c,na,nc)) continue;
if(conflict(b,c,nb,nc)) continue;
if(d[na][nb][nc]==-1)
{
d[na][nb][nc]=d[a][b][c]+1;
q.push(ID(na,nb,nc));
}
}
}
}
q.pop();
}
return false;
}
queue<int> p;
int back_bfs(){//反向BFS
int value;
int uu=p.front();
int aa=(uu>>16)&0xff,bb=(uu>>8)&0xff,cc=uu&0xff;
value=bd[aa][bb][cc];
while(!p.empty())
{
int u=p.front();
int a=(u>>16)&0xff,b=(u>>8)&0xff,c=u&0xff;
if(bd[a][b][c]!=value) return false;
if(d[a][b][c]!=-1) return true;
for(int i=0; i<deg[a]; i++)
{
int na=G[a][i];
for(int j=0; j<deg[b]; j++)
{
int nb=G[b][j];
for(int k=0; k<deg[c]; k++)
{
int nc=G[c][k];
if(conflict(a,b,na,nb)) continue;
if(conflict(a,c,na,nc)) continue;
if(conflict(b,c,nb,nc)) continue;
if(bd[na][nb][nc]==-1)
{
bd[na][nb][nc]=bd[a][b][c]+1;
p.push(ID(na,nb,nc));
}
}
}
}
p.pop();
}
return false;
}
int BFS(){
while(!q.empty()) q.pop();
while(!p.empty()) p.pop();
q.push(ID(s[0],s[1],s[2]));
p.push(ID(t[0],t[1],t[2]));
Memset();
d[s[0]][s[1]][s[2]]=0; bd[t[0]][t[1]][t[2]]=0;
int step=0,ok=0;
while(!p.empty()&&!q.empty()){//正向BFS与反向BFS交替进行，同时统计步数
if(bfs()){
ok=1;
break;
}
else step++;
if(back_bfs()){
ok=1;
break;
}
else step++;
}
return ok ? step:-1;
}
int main()
{
int w,h,n;
while(scanf("%d%d%d\n",&w,&h,&n)==3&&n!=0){
char maze[20][20];
for(int i=0;i<h;i++){
fgets(maze[i],20,stdin);
}
int cnt=0,x[256],y[256],id[20][20];
//将空地编上ID号
for(int i=0;i<h;i++){
for(int j=0;j<w;j++){
if(maze[i][j]!='#'){
x[cnt]=i;
y[cnt]=j;
id[i][j]=cnt;
if(islower(maze[i][j])){
s[maze[i][j] - 'a'] = cnt;
}
else if(isupper(maze[i][j])){
t[maze[i][j] - 'A'] = cnt;
}
cnt++;
}
}
}
//建图
for(int i=0;i<cnt;i++){
deg[i]=0;
for(int j=0;j<5;j++){
int nx = x[i]+dx[j], ny = y[i]+dy[j];
if(maze[nx][ny]!='#'){
G[i][deg[i]++]=id[nx][ny];
}
}
}
//不足三个鬼时添加鬼，方便统一处理
if(n<=2){
deg[cnt]=1;
G[cnt][0]=cnt;
s[2]=t[2]=cnt++;
}
if(n<=1){
deg[cnt]=1;
G[cnt][0]=cnt;
s[1]=t[1]=cnt++;
}
printf("%d\n",BFS());
}
return 0;
}