Top K Frequent Elements

c++

class element {
public:
    element() {}
    element(int a, int b) : key(a), cnt(b) {}
    int key;
    int cnt;
    inline bool operator<(const element &x) const { return cnt > x.cnt; }
};

class Solution {
public:
    vector<int> topKFrequent(vector<int>& nums, int k) {
        if (nums.empty()) return vector<int>();
        unordered_map<int, int> cache;
        for (auto &v : nums) {
            cache[v]++;
        }

        multiset dict;
        for (auto &v : cache) {
            dict.insert(element(v.first, v.second));
        }

        vector<int> res;
        int i = 0;
        for (auto &v : dict) {
            if (i++ == k) break;
            res.push_back(v.key);
        }
        return res;
    }
};

python

class Solution(object):
    def topKFrequent(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: List[int]
        """
        cache = collections.defaultdict(int)
        for v in nums:
            cache[v] += 1
        cache = sorted(cache.items(), key=lambda d: d[1]) [::-1]

        return [x[0] for x in itertools.islice(cache, k)]