HDU 5025

选拔赛(2)简单的状态压缩+bfs

屌洋直接用8维数组过的...代码美的一逼

 

题意：

　　悟空(K)找唐僧(T)，只能上下左右四个方向走，每步花费一个时间，碰到蛇精(S)需要额外花费一个时间去消灭，需要按照顺序(1, 2 ... k)搜集K把钥匙才能打开唐僧所在的房间。

　

总结：

　　在读入矩阵的时候，把每个S换成其他的字符，比如(a, b, c...)，这样再bfs的时候，碰到蛇精所在房间就可以直接判断当前蛇是否已经被杀死

　　任何题目中bfs的时候不能修改原有的矩阵数据，(后来的节点还会走到这个点上)

　　

if(a & b == 0){...}

if((a&b) == 0){...}

　　下面的表达式才能正确判断，运算符优先级(可以在任何时候都把位运算放在括号里面)

　　

#include <bits/stdc++.h>

const int MAXN = 100+5;

int n, k;
char ma[MAXN][MAXN];
// state compression
// the binary format of 31 is 11111
// there are at most 5 snakes in the maze
// so just use a binary digit bit to mark 
// weather it has been visited or not
// e.g. when wukong kills sankes numbered 1, 2, 5
// the statement will be 10011(19)

bool vis[MAXN][MAXN][10][32];

// for direction Wukong can go
int dir[4][2] = { {0, 1}, {0, -1}, {1, 0}, {-1, 0}};

struct QueNode
{
    int x, y, k, s, t;
    QueNode(){}
    // k is the number of keys wukong has 
    // s is the states of snakes (detail is the descriptioni of 'vis' above )
    // t is the time
    QueNode(int _x, int _y, int _k, int _s, int _t):x(_x), y(_y), k(_k), s(_s), t(_t){}

};

std::queue<QueNode> que;

int main()
{

    // this code below will clutter the output
    /* std::ios::sync_with_stdio(false); */
    
    while(std::cin >> n >> k && (n||k)){

        // init the variable
        // the efficient way to clear a std::queue
        // just create a empty_que and swap it with original queue
        memset(ma, '#', sizeof ma);
        memset(vis, false, sizeof vis);
        std::queue<QueNode> empty_que;
        std::swap(que, empty_que);

        // the highlight point 
        // dealing with the snakes 
        // rename it to enable it to show which snake it is
        int snake_num = 0; 
        
        for(int i = 1; i <= n; ++ i){
            for(int j = 1; j <= n; ++ j){
                std::cin >> ma[i][j];
                if(ma[i][j] == 'S'){
                    ma[i][j] = (++snake_num) + 'a';
                }
                if(ma[i][j] == 'K'){
                    que.push(QueNode(i, j, 0, 0, 0));
                    vis[i][j][0][0] = true;
                }
            }
        }

        bool ok = false;

        while(que.empty() == false){
            QueNode u = que.front();
            que.pop();
            // while wukong reaches the room in which Monk tang is
            // and wukong has enough keys
            if(ma[u.x][u.y] == 'T' && u.k == k){
                std::cout << u.t << std::endl;
                ok = true;
                break;
            }
            // if wukong enter the room with snake and has not killed the snake
            // it takes 1 minute to kill it 
            if(ma[u.x][u.y] <= 'a'+5 && ma[u.x][u.y] >= 'a'+1){
                int num = 1<<(ma[u.x][u.y] -'a'-1);
                
                /* if( u.s & num == 0) */
                // the statement above is wrong
                // pay attention to operator precedence
                if( (u.s&num) == 0){
                    u.s |= num;
                    ++ u.t;
                    que.push(u);
                    vis[u.x][u.y][u.k][u.s] = true;
                    continue;
                }
            }
            
            for(int i = 0; i < 4; ++ i){
                QueNode v(u);
                ++ v.t;
                v.x += dir[i][0];
                v.y += dir[i][1];

                if(ma[v.x][v.y] != '#'){
                    if(ma[v.x][v.y] - '0' == u.k + 1){
                        v.k = u.k + 1;
                    }
                    if(vis[v.x][v.y][v.k][v.s] == false){
                        vis[v.x][v.y][v.k][v.s] = true;
                        que.push(v);
                    }
                }
            }

        }
        if(ok == false){
            puts("impossible");
        }

    }

}