【HDOJ】3220 Alice’s Cube

状态压缩+逆向BFS。
方向数组就是任意相邻的两点（初始化时减1），每个顶点均有4个相邻点。因此，共有16*4/2=32个方向。按序排列即可找到。

/* 3220 */
#include <iostream>
#include <queue>
#include <algorithm>
#include <cstdio>
#include <cstring>
using namespace std;


char visit[1<<17];
const int end = 0x0ff;
int beg;
int dir[32][2] = {
    1,2, 1,3, 1,5, 1,9,
    2,4, 2,6, 2,10,
    3,4, 3,7, 3,11,
    4,8, 4,12,
    5,6, 5,7, 5,13,
    6,8, 6,14,
    7,8, 7,15,
    8,16,
    9,10, 9,11, 9,13,
    10,12, 10,14,
    11,12, 11,15,
    12,16,
    13,14, 13,15,
    14,16,
    15,16
};

void bfs() {
    int i, j, k, tmp;
    queue<int> Q;
    int a, b, s;
    char t;
    
    memset(visit, -1, sizeof(visit));
    visit[end] = 0;
    Q.push(end);
    
    while (!Q.empty()) {
        s = Q.front();
        Q.pop();
        t = visit[s];
        if (t >= 3)
            continue;
        ++t;
        for (i=0; i<32; ++i) {
            a = s & (1<<dir[i][0]);
            b = s & (1<<dir[i][1]);
            if (a ^ b) {
                tmp = (s ^ (1<<dir[i][0])) ^ (1<<dir[i][1]);                        
                if (visit[tmp] < 0) {
                    visit[tmp] = t;
                    Q.push(tmp);
                }
            }
        }
    }
}

void init() {
    int i;
    
    for (i=0; i<32; ++i) {
        --dir[i][0];
        --dir[i][1];
    }
    
    bfs();
}

int main() {
    int t, tt;
    int i, j, k;
    
    #ifndef ONLINE_JUDGE
        freopen("data.in", "r", stdin);
        freopen("data.out", "w", stdout);
    #endif
    
    init();
    scanf("%d", &tt);
    for (t=1; t<=tt; ++t) {
        beg = 0;
        for (i=15; i>=0; --i) {
            scanf("%d", &j);
            if (j)
                beg |= (1<<i);
        }
        k = visit[beg];
        if (k < 0)
            printf("Case #%d: more
", t);
        else
            printf("Case #%d: %d
", t, k);
    }
    
    return 0;
}