Most frequent number following key in an array

Array Hash Table Counting

59.4% acceptance

Feb 25, 2026

409

253

You are given a 0-indexed integer array nums. You are also given an integer key, which is present in nums. For every unique integer target in nums, count the number of times target immediately follows an occurrence of key in nums. Return the target with the maximum count.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn most_frequent(nums: Vec<i32>, key: i32) -> i32 {
    let mut count = [0i32; 1001];
    for i in 0..nums.len() - 1 {
      if nums[i] == key {
        count[nums[i + 1] as usize] += 1;
      }
    }
    count.iter().enumerate().max_by_key(|&(_, &c)| c).map(|(i, _)| i as i32).unwrap()
  }
}