hdu 4770(枚举 + dfs爆搜）

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题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4770

思路：由于最多只有15个"."，可以直接枚举放置的位置，然后判断是否能够全部点亮即可。需要注意的是，有一个特殊的light,也需要枚举它的位置以及放置的方向。

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int MAX_N = (200 + 22);int N, M;struct Node {int x, y;Node() {}Node(int _x, int _y) : x(_x), y(_y) {}}node[17];int n;char g[MAX_N][MAX_N];/*if kind == 0: 0 degree.if kind == 1: 90 degree.if kind == 2: 180 degree.if kind == 3: 270 degree.*/bool Judge(int x, int y){if (x < 0 || x >= N || y < 0 || y >= M) return true;if (g[x][y] == '.') return true;return false;}int find(int x, int y){for (int i = 0; i < n; ++i) {if (node[i].x == x && node[i].y == y) return i;}return -1;}bool vis[17];bool gao(int s, int kind){for (int i = 0; i < n; ++i) if ((1 << i) & s) {memset(vis, false, sizeof(vis));vis[i] = true;int x = node[i].x, y = node[i].y;if (kind == 0) {if (!Judge(x - 1, y) || !Judge(x, y + 1)) continue;if (x - 1 >= 0)vis[find(x - 1, y)] = true;if (y + 1 < M) vis[find(x, y + 1)] = true;} else if (kind == 1) {if (!Judge(x, y + 1) || !Judge(x + 1, y)) continue;if (y + 1 < M) vis[find(x, y + 1)] = true;if (x + 1 < N) vis[find(x + 1, y)] = true;} else if (kind == 2) {if (!Judge(x + 1, y) || !Judge(x, y - 1)) continue;if (x + 1 < N) vis[find(x + 1, y)] = true;if (y - 1 >= 0) vis[find(x, y - 1)] = true;} else if (kind == 3) {if (!Judge(x, y - 1) || !Judge(x - 1, y)) continue;if (y - 1 >= 0) vis[find(x, y - 1)] = true;if (x - 1 >= 0) vis[find(x - 1, y)] = true;}for (int j = 0; j < n; ++j) {if (j != i && ((1 << j) & s)) {x = node[j].x, y = node[j].y;vis[j] = true;if (!Judge(x - 1, y) || !Judge(x, y + 1)) break;if (x - 1 >= 0)vis[find(x - 1, y)] = true;if (y + 1 < M) vis[find(x, y + 1)] = true;}}bool tag = true;for (int i = 0; i < n; ++i) if (!vis[i]) {tag = false; break;}if (tag) return true;}return false;}int main(){while (~scanf("%d %d", &N, &M)) {if (N == 0 && M == 0) break;n = 0;for (int i = 0; i < N; ++i) {scanf("%s", g[i]);for (int j = 0; j < M; ++j) if (g[i][j] == '.') {node[n++] = Node(i, j);}}if (n == 0) {puts("0");continue;}int ans = -1;for (int s = 0; s < (1 << n); ++s) {for (int kind = 0; kind < 4; ++kind) {if (gao(s, kind)) {int x = s, cnt = 0;while (x) {++cnt;x &= (x - 1);}ans = (ans == -1 ? cnt : min(cnt, ans));}}}printf("%d\n", ans);}return 0;}

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