POJ 1753 位运算 + BFS

一道简单的BFS。由于只有16个点，所以只有2^16= 65536个状态。 当最终状态等于0或者65535时，即找到结果。

/* ID: sdj22251 PROG: lamps LANG: C++ */ #include <iostream> #include <vector> #include <list> #include <map> #include <set> #include <deque> #include <queue> #include <stack> #include <bitset> #include <algorithm> #include <functional> #include <numeric> #include <utility> #include <sstream> #include <iomanip> #include <cstdio> #include <cmath> #include <cstdlib> #include <cctype> #include <string> #include <cstring> #include <cmath> #include <ctime> #define MAX 2000000000 #define LOCA using namespace std; char s[6][6]; bool v[70000]; int turn[16] = {19, 39, 78, 140, 305, 626, 1252, 2248, 4880, 10016, 20032, 35968, 12544, 29184, 58368, 51200}; struct wwj { int tp; int num; wwj(){} wwj(int a, int b) { tp = a; num = b; } }q[77777]; int main() { #ifdef LOCAL freopen("lamps.in","r",stdin); freopen("lamps.out","w",stdout); #endif int i, j, tp = 0, ans = -1; for(i = 0; i < 4; i++) scanf("%s", s[i]); for(i = 0; i < 4; i++) { for(j = 0; j < 4; j++) { if(s[i][j] == 'w') tp |= (1 << (i * 4 + j)); } } int tail = 0, head = 0; wwj A(tp, 0); q[tail++] = A; v[A.tp] = true; while(head < tail) { wwj tmp = q[head++]; if(tmp.tp == 65535 || tmp.tp == 0) { ans = tmp.num; break; } for(i = 0; i < 16; i++) { wwj B(tmp.tp ^ turn[i], tmp.num + 1); if(v[B.tp] == false) { q[tail++] = B; v[B.tp] = true; } } } if(ans >= 0) printf("%d\n", ans); else printf("Impossible\n"); return 0; }