举几个使用 priority_queue的代码例子

以下是三个使用 priority_queue 的代码例子：

1. 求一组数中的前 k 大元素

int main() {
    int n = 10, k = 3;
    vector<int> nums = {3, 1, 4, 1, 5, 9, 2, 6, 5, 3};
    priority_queue<int, vector<int>, greater<int>> pq;
    for (int i = 0; i < n; i++) {
        pq.push(nums[i]);
        if (pq.size() > k) pq.pop();
    }
    while (!pq.empty()) {
        cout << pq.top() << " ";
        pq.pop();
    }
    return 0;
}

2. 最小的 k 个数

int main() {
    int n = 10, k = 3;
    vector<int> nums = {3, 1, 4, 1, 5, 9, 2, 6, 5, 3};
    priority_queue<int> pq;
    for (int i = 0; i < n; i++) {
        pq.push(nums[i]);
        if (pq.size() > k) pq.pop();
    }
    while (!pq.empty()) {
        cout << pq.top() << " ";
        pq.pop();
    }
    return 0;
}

3. 利用优先队列实现堆排序

void heap_sort(vector<int>& nums) {
    int n = nums.size();
    priority_queue<int, vector<int>, greater<int>> pq;
    for (int i = 0; i < n; i++) {
        pq.push(nums[i]);
    }
    int i = 0;
    while (!pq.empty()) {
        nums[i++] = pq.top();
        pq.pop();
    }
}