Top K Frequent Elements Problem


Description

LeetCode Problem 347.

Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order.

Example 1:

1
2
Input: nums = [1,1,1,2,2,3], k = 2
Output: [1,2]

Example 2:

1
2
Input: nums = [1], k = 1
Output: [1]

Constraints:

  • 1 <= nums.length <= 10^5
  • k is in the range [1, the number of unique elements in the array].
  • It is guaranteed that the answer is unique.


Sample C++ Code

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
class Solution {
public:
    static bool cmp (const pair<int, int> &a, const pair<int, int> &b) {
        return a.second > b.second;
    }
    vector<int> topKFrequent(vector<int>& nums, int k) {
        unordered_map<int, int> ht;
        vector<pair<int, int>> v;
        for (int i = 0; i < nums.size(); i ++) {
            if (ht.find(nums[i]) == ht.end())
                ht[nums[i]] = 0;
            ht[nums[i]] ++;
        }
        for (auto m : ht) {
            v.push_back({m.first, m.second});
        }
        sort(v.begin(), v.end(), cmp);
        
        vector<int> ans;
        for (int i = 0; i < k; i ++) {
            ans.push_back(v[i].first);
        }
        
        return ans;
    }
};




Related Posts

Find Duplicate Subtrees Problem

LeetCode 652. Given the rootof a binary tree, return all...

Delete And Earn Problem

LeetCode 740. You are given an integer array nums. You...

Degree Of An Array Problem

LeetCode 697. Given a non-empty array of non-negative integers nums,...

Custom Sort String Problem

LeetCode 791. You are given two strings order and s....

Basic Calculator IV Problem

LeetCode 770. Given an expression such as expression = “e...

Sort Characters By Frequency Problem

LeetCode 451. Given a string s, sort it in decreasing...