Ural 1060. Flip Game

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<vector>
#include<set>
#include<queue>
#include<map>
#include<sstream>
#include<iostream>
using namespace std;

#define FOR(i,a,b) for(int (i)=(a);(i)<=(b);(i)++)
#define DOR(i,a,b) for(int (i)=(a);(i)>=(b);(i)--)
#define bug puts("Fuck");
#define LL long long
#define pb push_back
#define mp make_pair

#define nMax 1<<17
#define eps 1e-8
#define inf 0x7fffffff

int dp[nMax],vis[nMax];
char s[5][5];
queue<int> que;
int bfs(int n){
while(!que.empty()) que.pop();
dp[0]=dp[n-1]=0;
que.push(0),que.push(n-1);
vis[0]=vis[n-1]=1;
while(!que.empty()){
int cur = que.front();que.pop();
for(int i=0;i<16;i++) {
int b=cur^(1<<i);
if(i>3) b^=(1<<(i-4));
if(i%4!=0) b^=(1<<(i-1));
if(i%4!=3) b^=(1<<(i+1));
if(i<12)   b^=(1<<(i+4));
if(dp[b]==-1 || dp[b]>dp[cur]+1) {
dp[b]=dp[cur]+1;
if(!vis[b]) {
vis[b]=1;
que.push(b);
}
}
}
}

}
void init(){
int n=(1<<16);
for(int i=0;i<n;i++) dp[i]=-1,vis[i]=0;
bfs(n);
}
int main(){
#ifndef ONLINE_JUDGE
//	freopen("input.txt","r",stdin);
//	freopen("output.txt","w",stdout);
#endif
init();
for(int i=0;i<4;i++) scanf("%s",s[i]);
int cur=0;
for(int i=0;i<4;i++) for(int j=0;j<4;j++) if(s[i][j]=='w') cur += (1<<(4*i+j));
if(dp[cur]==-1) printf("Impossible\n");
else printf("%d\n",dp[cur]);

return 0;
}