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pojcs101_M01328_radar_greedy.cpp

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+#include <iostream>
+#include <vector>
+#include <cmath>
+#include <algorithm>
+
+using namespace std;
+
+double other_leg(const double leg, const double diag) {
+    return sqrt(diag * diag - leg * leg);
+}
+
+double diag(const double leg1, const double leg2) {
+    return sqrt(leg1 * leg1 + leg2 * leg2);
+}
+
+vector<pair<double, double>> target_ranges(vector<pair<int, int>> islands, const int distance) {
+    vector<pair<double, double>> ranges;
+    for (auto& [island_x, island_y] : islands) {
+        if (island_y > distance) { throw std::runtime_error("Island is too far away from the radar."); }
+        const double offset = other_leg(island_y, distance);
+        ranges.emplace_back(island_x - offset, island_x + offset);
+    }
+    sort(ranges.begin(), ranges.end(),
+         [](const auto& a, const auto& b) { return a.second < b.second; });
+    return ranges;
+}
+
+int required_radars(const vector<pair<double, double>>& ranges) {
+    if (ranges.empty()) { return 0; }
+    int answer = 1;
+    double current_max_x = ranges[0].second;
+    for (const auto& [left,right] : ranges) {
+        if (left > current_max_x) { answer++, current_max_x = right; } // 放不下，加雷达
+        else if (right < current_max_x) { current_max_x = right; } // 放下，需要左移雷达
+        clog << "current_max_x: " << current_max_x << " answer: " << answer << endl;
+    }
+    return answer;
+}
+
+int main() {
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int n, distance, case_id = 0;
+    while (cin >> n >> distance) {
+        if (n == 0 && distance == 0) { break; }
+        vector<pair<int, int>> islands(n);
+        for (int i = 0; i < n; i++) {
+            cin >> islands[i].first >> islands[i].second;
+        }
+        // cout << "Case " << ++case_id << ": ";
+        try {
+            cout << required_radars(target_ranges(islands, distance)) << endl;
+        } catch (std::runtime_error&) {
+            cout << -1 << endl;
+        }
+    }
+}
+