[C++] STL Priority_queue（優先佇列容器適配器）

#include <queue>
#include <iostream>

int main() {
    // 預設：最大堆
    std::priority_queue<int> maxHeap;

    maxHeap.push(30);
    maxHeap.push(10);
    maxHeap.push(50);
    maxHeap.push(20);

    std::cout << "最大堆頂: " << maxHeap.top() << std::endl;  // 50

    // 逐個彈出（降序）
    while (!maxHeap.empty()) {
        std::cout << maxHeap.top() << " ";
        maxHeap.pop();
    }
    // 輸出: 50 30 20 10

    return 0;
}

#include <queue>
#include <vector>
#include <functional>
#include <iostream>

int main() {
    // 最小堆
    std::priority_queue<int, std::vector<int>, std::greater<int>> minHeap;

    minHeap.push(30);
    minHeap.push(10);
    minHeap.push(50);
    minHeap.push(20);

    std::cout << "最小堆頂: " << minHeap.top() << std::endl;  // 10

    // 逐個彈出（升序）
    while (!minHeap.empty()) {
        std::cout << minHeap.top() << " ";
        minHeap.pop();
    }
    // 輸出: 10 20 30 50

    return 0;
}

#include <queue>
#include <vector>
#include <iostream>

std::vector<int> topKFrequent(const std::vector<int>& nums, int k) {
    // 使用最小堆維護前 k 大的頻率
    auto cmp = [](const std::pair<int, int>& a, const std::pair<int, int>& b) {
        return a.second > b.second;  // 最小堆
    };

    std::priority_queue<std::pair<int, int>,
                        std::vector<std::pair<int, int>>,
                        decltype(cmp)> minHeap(cmp);

    // 統計頻率（簡化示例）
    std::unordered_map<int, int> freq = {{1, 3}, {2, 2}, {3, 1}};

    for (const auto& [num, count] : freq) {
        minHeap.push({num, count});
        if (minHeap.size() > k) {
            minHeap.pop();
        }
    }

    std::vector<int> result;
    while (!minHeap.empty()) {
        result.push_back(minHeap.top().first);
        minHeap.pop();
    }

    return result;
}

int main() {
    std::vector<int> nums = {1, 1, 1, 2, 2, 3};
    int k = 2;

    auto result = topKFrequent(nums, k);

    std::cout << "前 " << k << " 高頻元素: ";
    for (int num : result) {
        std::cout << num << " ";
    }

    return 0;
}

#include <queue>
#include <iostream>

struct Task {
    int priority;
    std::string name;

    Task(int p, const std::string& n) : priority(p), name(n) {}
};

// 自訂比較（優先級高的在前）
struct TaskCompare {
    bool operator()(const Task& a, const Task& b) const {
        return a.priority < b.priority;  // 注意：小於號表示最大堆
    }
};

int main() {
    std::priority_queue<Task, std::vector<Task>, TaskCompare> taskQueue;

    taskQueue.push(Task(3, "低優先級"));
    taskQueue.push(Task(10, "高優先級"));
    taskQueue.push(Task(5, "中優先級"));

    while (!taskQueue.empty()) {
        auto task = taskQueue.top();
        std::cout << "執行: " << task.name
                  << " (優先級: " << task.priority << ")" << std::endl;
        taskQueue.pop();
    }

    return 0;
}