P2895 [USACO08FEB]Meteor Shower S

R43077831

problem/P2895/P2895.cpp

@@ -0,0 +1,60 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+const int dx[] = {0, 0, 0, -1, 1};
+const int dy[] = {0, 1, -1, 0, 0};
+
+struct node {
+    int x, y, t;
+
+    node() {
+        x = y = t = 0;
+    }
+    node(int _x, int _y, int _t) {
+        x = _x, y = _y, t = _t;
+    }
+};
+
+int n, x, y, t, m[305][305], f[305][305];
+
+int main() {
+    memset(m, 0x3f, sizeof(m));
+    cin >> n;
+    for (int i = 1; i <= n; i++) {
+        cin >> x >> y >> t;
+        m[x][y] = min(m[x][y], t);
+        for (int j = 1; j <= 4; j++) {
+            int xx = x + dx[j];
+            int yy = y + dy[j];
+            if (xx < 0 || yy < 0) continue;
+            m[xx][yy] = min(m[xx][yy], t);
+        }
+    }
+    queue<node> q;
+    f[0][0] = 1;
+    if (m[0][0] == 0x3f3f3f3f) {
+        cout << 0 << endl;
+        return 0;
+    }
+    q.push(node(0, 0, 0));
+    while (!q.empty()) {
+        int xx = q.front().x;
+        int yy = q.front().y;
+        int tt = q.front().t;
+        q.pop();
+        for (int i = 1; i <= 4; i++) {
+            int u = xx + dx[i];
+            int v = yy + dy[i];
+            if (f[u][v] || u < 0 || v < 0 || tt + 1 >= m[u][v]) continue;
+            if (m[u][v] == 0x3f3f3f3f) {
+                cout << tt + 1 << endl;
+                return 0;
+            }
+            q.push(node(u, v, tt + 1));
+            f[u][v] = 1;
+        }
+    }
+    cout << -1 << endl;
+    return 0;
+}