HDU 5040 Instrusive（北京網路賽I題）

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HDU 5040 Instrusive

題目連結

思路：記憶化廣搜，先預先處理出圖，每個位置用一個位元表示，表示4秒為1個周期內，這個位置是否會被照到，然後進行記憶化廣搜即可，狀態多開一個4，表示在4秒一周期，然後進行轉移即可

代碼：

#include <cstdio>#include <cstring>#include <queue>using namespace std;const int N = 505;const int d[4][2] = {-1, 0, 0, 1, 1, 0, 0, -1};int t, n;int g[N][N], vis[N][N][5];struct State {int x, y, t;State() {}State(int x, int y, int t) {this->x = x;this->y = y;this->t = t;}} s, e;int get(char c) {if (c == 'N') return 0;if (c == 'E') return 3;if (c == 'S') return 2;if (c == 'W') return 1;return -1;}const int INF = 0x3f3f3f3f;char str[N][N];int solve() {queue<State> Q;Q.push(s);memset(vis, INF, sizeof(vis));vis[s.x][s.y][s.t] = 0;while (!Q.empty()) {State u = Q.front();Q.pop();State v = u;v.t = (v.t + 1) % 4;if (vis[v.x][v.y][v.t] > vis[u.x][u.y][u.t] + 1) {vis[v.x][v.y][v.t] = vis[u.x][u.y][u.t] + 1;Q.push(v);}for (int i = 0; i < 4; i++) {State v = u;v.x = u.x + d[i][0];v.y = u.y + d[i][1];int add = 0;if (v.x < 0 || v.x >= n || v.y < 0 || v.y >= n || g[v.x][v.y] == -1) continue;if ((g[u.x][u.y]&(1<<u.t)) || (g[v.x][v.y]&(1<<u.t))) {v.t = (v.t + 3) % 4;add = 3;} else {v.t = (v.t + 1) % 4;add = 1;}if (vis[v.x][v.y][v.t] > vis[u.x][u.y][u.t] + add) {vis[v.x][v.y][v.t] = vis[u.x][u.y][u.t] + add;Q.push(v);}}}int ans = INF;for (int i = 0; i < 4; i++)ans = min(ans, vis[e.x][e.y][i]);if (ans == INF) ans = -1;return ans;}int main() {int cas = 0;scanf("%d", &t);while (t--) {scanf("%d", &n);for (int i = 0; i < n; i++)scanf("%s", str[i]);memset(g, 0, sizeof(g));for (int i = 0; i < n; i++) {for (int j = 0; j < n; j++) {if (str[i][j] == 'M')s = State(i, j, 0);else if (str[i][j] == 'T')e = State(i, j, 0);else if (str[i][j] == '#')g[i][j] = -1;else if (str[i][j] == 'N' || str[i][j] == 'E' || str[i][j] == 'S' || str[i][j] == 'W') {g[i][j] = 15;for (int k = 0; k < 4; k++) {int x = i + d[k][0];int y = j + d[k][1];if (x < 0 || x >= n || y < 0 || y >= n || str[x][y] == '#') continue;g[x][y] |= (1<<((get(str[i][j]) + k) % 4));}}}}printf("Case #%d: %d\n", ++cas, solve());}return 0;}

HDU 5040 Instrusive（北京網路賽I題）