[hihoCoder] 题外话·堆

A direct applicatin of the heap data structure. Specifically, a max heap is used. The required functions include insertion of a node to the heap and extraction of the maximum element of the heap. Each time you insert or remove an element to or from the heap, you need to maintain the max heap property.

The code is as follows.

If you want to learn more about heap, you may refer to this passage.

#include <iostream>
#include <vector>

using namespace std;

class Heap {
public:
    Heap() {
        data.clear();
    }

    inline int parent(int idx) {
        return (idx - 1) >> 1;
    }

    inline int left(int idx) {
        return (idx << 1) + 1;
    }

    inline int right(int idx) {
        return (idx << 1) + 2;
    }

    void max_heapify(int idx) {
        int largest = idx;
        int l = left(idx), r = right(idx);
        if (l < (int)data.size() && data[l] > data[largest]) largest = l;
        if (r < (int)data.size() && data[r] > data[largest]) largest = r;
        if (largest != idx) {
            swap(data[idx], data[largest]);
            max_heapify(largest);
        }
    }

    void insert(int elem) {
        data.push_back(elem);
        int idx = data.size() - 1;
        while (idx >= 0 && parent(idx) >= 0 && data[parent(idx)] < data[idx]) {
            swap(data[parent(idx)], data[idx]);
            idx = parent(idx);
        }
    }

    int extract_max(void) {
        int maximum = data[0];
        swap(data[0], data[data.size() - 1]);
        data.erase(data.end() - 1, data.end());
        max_heapify(0);
        return maximum;
    }

private:
    vector<int> data;
};

int main(void) {
    int events;
    while (scanf("%d", &events) != EOF) {
        Heap sugars;
        for (int i = 0; i < events; i++) {
            char order[2];
            scanf("%s", order);
            if (order[0] == 'A') {
                int sugar;
                scanf("%d", &sugar);
                sugars.insert(sugar);
            }
            else printf("%d\n", sugars.extract_max());
        }
    }
    return 0;
}