#2633. 「BalticOI 2011 Day1」宝藏与维京海盗 Treasures and Vikings

https://loj.ac/s/1307430

LibreOJ/2633/2633.cpp

@@ -0,0 +1,134 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+const int to[4][2] = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
+
+int n, m, book[705][705];
+bool vis[705][705];
+char g[705][705];
+pair<int, int> y, v, t;
+
+struct node {
+    int x, y, step;
+
+    node()
+        : x(0), y(0), step(0) {}
+    node(int _x, int _y)
+        : x(_x), y(_y), step(0) {}
+    node(pair<int, int> _point)
+        : x(_point.first), y(_point.second), step(0) {}
+    node(pair<int, int> _point, int _step)
+        : x(_point.first), y(_point.second), step(_step) {}
+    node(int _x, int _y, int _step)
+        : x(_x), y(_y), step(_step) {}
+};
+
+/**
+ * @brief Preprocess the map
+ */
+void bfsV() {
+    memset(vis, 0x00, sizeof(vis));
+    memset(book, 0xff, sizeof(book));
+    queue<node> q;
+    q.push(v);
+    vis[v.first][v.second] = true;
+    book[v.first][v.second] = 0;
+    while (!q.empty()) {
+        int now;
+        auto u = q.front();
+        q.pop();
+
+        // Top
+        now = u.x - 1;
+        while (now >= 0 && g[now][u.y] != 'I') {
+            if (book[now][u.y] == -1) {
+                book[now][u.y] = u.step;
+            }
+            now--;
+        }
+
+        // Bottom
+        now = u.x + 1;
+        while (now < n && g[now][u.y] != 'I') {
+            if (book[now][u.y] == -1) {
+                book[now][u.y] = u.step;
+            }
+            now++;
+        }
+
+        // Left
+        now = u.y - 1;
+        while (now >= 0 && g[u.x][now] != 'I') {
+            if (book[u.x][now] == -1) {
+                book[u.x][now] = u.step;
+            }
+            --now;
+        }
+
+        // Right
+        now = u.y + 1;
+        while (now < m && g[u.x][now] != 'I') {
+            if (book[u.x][now] == -1) {
+                book[u.x][now] = u.step;
+            }
+            now++;
+        }
+
+        // Expand
+        for (int i = 0; i < 4; i++) {
+            node e = node(u.x + to[i][0], u.y + to[i][1], u.step + 1);
+            if (e.x >= 0 && e.x < n && e.y >= 0 && e.y < m && g[e.x][e.y] != 'I' && !vis[e.x][e.y]) {
+                vis[e.x][e.y] = true;
+                q.push(e);
+            }
+        }
+    }
+}
+
+/**
+ * @brief Search path to treasure
+ */
+void bfsY() {
+    memset(vis, 0x00, sizeof(vis));
+    queue<node> q;
+    q.push(node(y, 1));
+    while (!q.empty()) {
+        auto u = q.front();
+        q.pop();
+        for (int i = 0; i < 4; i++) {
+            node e = node(u.x + to[i][0], u.y + to[i][1], u.step + 1);
+            if (e.x >= 0 && e.x < n && e.y >= 0 && e.y < m && e.step <= book[e.x][e.y] && !vis[e.x][e.y]) {
+                vis[e.x][e.y] = true;
+                // Reached
+                if (e.x == t.first && e.y == t.second) {
+                    cout << "YES" << endl;
+                    return;
+                }
+                // Expand
+                q.push(e);
+            }
+        }
+    }
+    // Can't reach treasure
+    cout << "NO" << endl;
+}
+
+int main() {
+    // Read from stdin
+    cin >> n >> m;
+    for (int i = 0; i < n; i++) {
+        cin >> g[i];
+    }
+    // Mark you, viking and treasure
+    for (int i = 0; i < n; i++) {
+        for (int j = 0; j < m; j++) {
+            if (g[i][j] == 'Y') y = make_pair(i, j);
+            if (g[i][j] == 'V') v = make_pair(i, j);
+            if (g[i][j] == 'T') t = make_pair(i, j);
+        }
+    }
+    bfsV();
+    bfsY();
+    return 0;
+}