zoj 1649 Rescue

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=649

 

BFS题.纠结了很久.这题不是无权最短路径的题.而是有权的.然后就用一般的BFS做了,WA多次.后来看了别人的解题报告才知道处理guard时

 

要分别对待.

 

/* * 2050.cpp * * Created on: Apr 29, 2010 * Author: wyy * */#include<cstdio>#include<queue>using namespace std;char graph[4][5];bool marked[65536];int N, State;int dx[4] = {0, 0, 1, -1};int dy[4] = {1, -1, 0, 0};struct point{int state, ret;};bool IsValid(int x, int y){return (x >= 0 && x < 4 && y >= 0 && y < 4);}void Init(){State = 0;for(int i = 0; i < 65536; ++i)marked[i] = false;for(int i = 0; i < 4; ++i){getchar();scanf("%s", graph[i]);for(int j = 0; j < 4; ++j)if(graph[i][j] == 'b')State |= 1 << (4 * i + j);}}void BFS(){queue<point> Q;bool flag = false;point p1, p2;p1.state = State;p1.ret = 0;marked[p1.state] = true;Q.push(p1);while(!Q.empty()){p1 = Q.front();Q.pop();if(p1.state == 0 || p1.state == 65535){printf("%d/n", p1.ret);flag = true;break;}for(int i = 0; i < 16; ++i){p2.state = p1.state ^ (1 << i);for(int j = 0; j < 4; ++j)if(IsValid(i / 4 + dx[j], i % 4 + dy[j]))p2.state ^= (1 << (i + 4 * dx[j] + dy[j]));if(!marked[p2.state]){marked[p2.state] = true;p2.ret = p1.ret + 1;Q.push(p2);}}}if(!flag)printf("Impossible/n");if(N)printf("/n");}int main(){//freopen("input.txt", "r", stdin);scanf("%d", &N);while(N--){Init();BFS();}//fclose(stdin);return 0;}