poj 1475 Pushing Boxes

#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <queue>
using namespace std;
const int maxn = 22;
char map[maxn][maxn];
bool visPerson[maxn][maxn];
bool visBox[maxn][maxn];
int R , C;
int dir[4][2] = { {0,1},{0,-1},{1,0},{-1,0} };
char pushes[4] = { 'E','W','S','N' };
char walks[4] = { 'e','w','s','n' };
string path;
struct Node{
int br , bc , pr , pc;
string ans;
};
bool inMap(int r , int c) {
return r>=0 && r<R && c>=0 && c<C;
}
bool bfs2(int sr, int sc, int er, int ec, int br, int bc, string &ans) {
Node node , tmpnode;
memset(visPerson,0,sizeof(visPerson));
queue<Node> Q;
node.pr = sr;
node.pc = sc;
node.ans = "";
Q.push(node);
visPerson[br][bc] = true;
while(!Q.empty()) {
node = Q.front();  Q.pop();
if(node.pr == er && node.pc == ec) {
ans = node.ans;
return true;
}
if(visPerson[node.pr][node.pc]) continue;
visPerson[node.pr][node.pc] = true;
for(int i=0;i<4;i++) {
int nr = node.pr + dir[i][0];
int nc = node.pc + dir[i][1];
if(inMap(nr,nc) && !visPerson[nr][nc] && map[nr][nc]!='#') {
tmpnode.pr = nr;
tmpnode.pc = nc;
tmpnode.ans =node.ans + walks[i];
Q.push(tmpnode);
}
}
}
return false;
}
bool bfs1(int sr ,int sc, int br, int bc) {
Node node , tmpnode;
memset(visBox,0,sizeof(visBox));
queue<Node> Q;
node.pr = sr;
node.pc = sc;
node.br = br;
node.bc = bc;
node.ans = "";
Q.push(node);
while(!Q.empty()) {
node = Q.front();  Q.pop();
if(visBox[node.br][node.bc])
continue;
visBox[node.br][node.bc] = true;
if(map[node.br][node.bc]=='T') {
path = node.ans;
return true;
}
visBox[node.br][node.bc] = true;
for(int i=0;i<4;i++) {
int nextr = node.br + dir[i][0];
int nextc = node.bc + dir[i][1];
int backr = node.br - dir[i][0];
int backc = node.bc - dir[i][1];
string ans = "";
if( inMap(nextr,nextc) && inMap(backr,backc)
&& map[nextr][nextc]!='#' && map[backr][backc]!='#'
&& !visBox[nextr][nextc] ) {
if(bfs2(node.pr, node.pc, backr, backc, node.br, node.bc, ans)) {
tmpnode.pr = node.br;
tmpnode.pc = node.bc;
tmpnode.br = nextr;
tmpnode.bc = nextc;
tmpnode.ans = node.ans +ans +pushes[i];
Q.push(tmpnode);
}
}
}
}
return false;
}
int main() {
int cas = 1;
int sr , sc , br , bc;
while(~scanf("%d%d",&R,&C) && R) {
for(int i=0;i<R;i++) scanf("%s",map[i]);
for(int i=0;i<R;i++)
for(int j=0;j<C;j++) {
if(map[i][j]=='S') {
sr = i; sc = j;
}
if(map[i][j]=='B') {
br = i; bc = j;
}
}
path = "";
printf("Maze #%d\n",cas++);
bfs1(sr,sc,br,bc) ? cout<<path<<endl : cout<<"Impossible."<<endl;
cout<<endl;
}
return 0;
}