P4442 [COCI2017-2018#3] Portal

https://www.luogu.com.cn/record/100633119

Luogu/P4442/P4442.cpp

@@ -0,0 +1,181 @@
+#include <iostream>
+#include <cstring>
+#include <queue>
+#include <string>
+#include <utility>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 505;
+const int INF = 0x3f3f3f3f;
+const int d[][2] = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
+
+int n, m, s, t, pos[N * N][4], dist1[N][N], dist2[N * N];
+std::string h[N];
+std::vector<std::pair<int, int>> g[N * N];
+bool vis[N * N];
+
+int id(int x, int y) {
+    return x * m + y;
+}
+
+void spfa() {
+    memset(dist2, 0x3f, sizeof(dist2));
+
+    std::queue<int> q;
+
+    q.emplace(s);
+    dist2[s] = 0;
+    vis[s] = true;
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+
+        vis[u] = false;
+
+        for (auto e : g[u]) {
+            int v = e.first;
+            long long w = e.second;
+
+            if (dist2[v] > dist2[u] + w) {
+                dist2[v] = dist2[u] + w;
+
+                if (!vis[v]) {
+                    vis[v] = true;
+
+                    q.emplace(v);
+                }
+            }
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    memset(dist1, 0x3f, sizeof(dist1));
+
+    cin >> n >> m;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> h[i];
+
+        h[i] = ' ' + h[i];
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= m; j++) {
+            if (h[i][j] == 'C') {
+                s = id(i, j);
+            } else if (h[i][j] == 'F') {
+                t = id(i, j);
+            }
+        }
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= m; j++) {
+            if (h[i][j - 1] == '#') {
+                pos[id(i, j)][0] = id(i, j);
+            } else {
+                pos[id(i, j)][0] = pos[id(i, j - 1)][0];
+            }
+        }
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = m; j; j--) {
+            if (h[i][j + 1] == '#') {
+                pos[id(i, j)][1] = id(i, j);
+            } else {
+                pos[id(i, j)][1] = pos[id(i, j + 1)][1];
+            }
+        }
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= m; j++) {
+            if (h[i - 1][j] == '#') {
+                pos[id(i, j)][2] = id(i, j);
+            } else {
+                pos[id(i, j)][2] = pos[id(i - 1, j)][2];
+            }
+        }
+    }
+
+    for (int i = n; i; i--) {
+        for (int j = 1; j <= m; j++) {
+            if (h[i + 1][j] == '#') {
+                pos[id(i, j)][3] = id(i, j);
+            } else {
+                pos[id(i, j)][3] = pos[id(i + 1, j)][3];
+            }
+        }
+    }
+
+    std::queue<std::pair<int, int>> q;
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= m; j++) {
+            if (h[i][j] == '#') {
+                q.emplace(i, j);
+                dist1[i][j] = 0;
+            }
+        }
+    }
+
+    while (!q.empty()) {
+        int x = q.front().first,
+            y = q.front().second;
+        q.pop();
+
+        for (auto d : d) {
+            int xx = x + d[0],
+                yy = y + d[1];
+
+            if (xx < 1 || xx > n || yy < 1 || yy > m || h[xx][yy] == '#') continue;
+
+            if (dist1[xx][yy] > dist1[x][y] + 1) {
+                dist1[xx][yy] = dist1[x][y] + 1;
+
+                q.emplace(xx, yy);
+            }
+        }
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= m; j++) {
+            if (h[i][j] == '#') continue;
+
+            for (auto d : d) {
+                int x = i + d[0],
+                    y = j + d[1];
+
+                if (h[x][y] != '#') {
+                    g[id(i, j)].emplace_back(id(x, y), 1);
+                }
+            }
+
+            for (int k = 0; k < 4; k++) {
+                if (pos[id(i, j)][k] != id(i, j)) {
+                    g[id(i, j)].emplace_back(pos[id(i, j)][k], dist1[i][j]);
+                }
+            }
+        }
+    }
+
+    spfa();
+
+    if (dist2[t] == INF) {
+        cout << "nemoguce" << endl;
+    } else {
+        cout << dist2[t] << endl;
+    }
+
+    return 0;
+}