P2498 [SDOI2012]拯救小云公主

https://www.luogu.com.cn/record/85636345

Luogu/P2498/P2498.cpp

@@ -0,0 +1,74 @@
+#include <iostream>
+#include <algorithm>
+#include <cmath>
+#include <iomanip>
+#include <queue>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 3005;
+const double eps = 1e-4;
+
+int n, row, line;
+std::pair<int, int> a[N];
+bool vis[N];
+
+bool check(double x) {
+    std::fill_n(vis, N, false);
+
+    std::queue<int> q;
+
+    for (int i = 1; i <= n; i++) {
+        if (a[i].first - 1 < x || line - a[i].second < x) {
+            vis[i] = true;
+            q.push(i);
+        }
+    }
+
+    while (!q.empty()) {
+        auto u = q.front();
+        q.pop();
+
+        if (row - a[u].first < x || a[u].second - 1 < x) {
+            return false;
+        }
+
+        for (int i = 1; i <= n; i++) {
+            if (!vis[i] && std::sqrt(std::pow(a[u].first - a[i].first, 2) + std::pow(a[u].second - a[i].second, 2)) < x * 2) {
+                vis[i] = true;
+                q.push(i);
+            }
+        }
+    }
+
+    return true;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> row >> line;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i].first >> a[i].second;
+    }
+
+    double l = 0, r = std::min(row, line);
+
+    while (r - l > eps) {
+        double mid = (l + r) / 2;
+
+        if (check(mid)) {
+            l = mid;
+        } else {
+            r = mid;
+        }
+    }
+
+    cout << std::fixed << std::setprecision(2) << l << endl;
+
+    return 0;
+}