README.md

347. Top K Frequent Elements

Given a non-empty array of integers, return the k most frequent elements.

Example 1:

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

Example 2:

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

Note:

• You may assume k is always valid, 1 ≤ k ≤ number of unique elements.
• Your algorithm's time complexity must be better than O(n log n), where n is the array's size.
• It's guaranteed that the answer is unique, in other words the set of the top k frequent elements is unique.
• You can return the answer in any order.

Solutions (Rust)

1. Sort

use std::collections::HashMap;

impl Solution {
    pub fn top_k_frequent(nums: Vec<i32>, k: i32) -> Vec<i32> {
        let mut counter = HashMap::new();

        for num in nums {
            *counter.entry(num).or_insert(0) += 1;
        }

        let mut counter = counter.iter().collect::<Vec<_>>();

        counter.sort_unstable_by_key(|c| c.1);

        counter
            .iter()
            .rev()
            .take(k as usize)
            .map(|(k, v)| **k)
            .collect()
    }
}