TopKFrequentElements

Mon, 02 Mar 2026 00:35:15 +0800

TopKFrequentElements

Difficulty: Medium
Topics: Hash Table, Heap, Frequency Counting

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

Approach

This problem asks us to find the k most frequent elements. We first use an unordered_map to count the frequency of each element. Then we use a min-heap of size k to maintain the current top-k elements. When the heap size exceeds k, we remove the smallest element. Finally, we obtain a list of size k that contains the top-k elements.

C++ STL Cheatsheet

Sun, 01 Mar 2026 23:08:29 +0800

C++ STL Cheatsheet

STL (Standard Template Library) provides generic containers and algorithms for C++ development. This note summarizes commonly used containers, typical usage patterns, and pitfalls.

Headers (common)

#include <vector>
#include <array>
#include <string>
#include <deque>
#include <list>
#include <forward_list>

#include <queue>
#include <stack>

#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>

#include <algorithm>
#include <utility>
#include <tuple>
#include <bitset>

Vector

Dynamic array with contiguous memory.

vector<int> v = {1,2,3};
v.push_back(4);
v.emplace_back(5);

int x = v[0];
v.pop_back();

Notes

Random access: O(1)
Insert/erase in middle: O(n)
reserve(n) reduces reallocations
Iterator invalidation: reallocation invalidates all iterators/pointers/references

Array

Fixed-size array (stack-friendly, no dynamic allocation).

Programming on mizu-blog

TopKFrequentElements

TopKFrequentElements

Approach

C++ STL Cheatsheet

C++ STL Cheatsheet

Headers (common)

Vector

Array