LeetCode/LeetCode-347 at master · lwp-6/LeetCode · GitHub

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/*
找出数组nums中出现频率最高的k个元素
哈希表+大顶堆
*/
class Solution {
public:
    map<int, int> m;
    vector<int> topKFrequent(vector<int>& nums, int k) {
        int i, cur;

        vector<int> queue, v;
        for(i = 0; i < nums.size(); ++i)
        {
            m[nums[i]]++;
        }
        sort(nums.begin(), nums.end());
        nums.erase(unique(nums.begin(), nums.end()), nums.end());
        for(i = 0; i < nums.size(); ++i)
        {
            queue.push_back(nums[i]);
        }
        cur = (nums.size()-2) / 2;
        while(cur >= 0)
        {
            siftdown(queue, cur);
            cur--;
        }

        for (i = 0; i < k; ++i)
        {
            v.push_back(queue[0]);
            queue[0] = queue[queue.size() - 1];
            queue.pop_back();
            siftdown(queue, 0);
        }
        return v;
    }
    void siftdown(vector<int>& queue, int pos)
    {
        int temp;

        if ((2 * pos + 2) < queue.size() && (2 * pos + 1) < queue.size())
        {
            temp = max(max(m[queue[2 * pos + 2]], m[queue[2 * pos + 1]]), m[queue[pos]]);
            if (temp == m[queue[2 * pos + 2]])
            {
                swap(queue[pos], queue[2 * pos + 2]);
                siftdown(queue, 2 * pos + 2);
            }
            else if (temp == m[queue[2 * pos + 1]])
            {
                swap(queue[pos], queue[2 * pos + 1]);
                siftdown(queue, 2 * pos + 1);
            }
        }
        else if ((2 * pos + 1) < queue.size())
        {
            if (m[queue[pos]] < m[queue[2 * pos + 1]])
            {
                swap(queue[pos], queue[2 * pos + 1]);
                siftdown(queue, 2 * pos + 1);
            }
        }

    }
};