README.md

2150. Find All Lonely Numbers in the Array

You are given an integer array nums. A number x is lonely when it appears only once, and no adjacent numbers (i.e. x + 1 and x - 1) appear in the array.

Return all lonely numbers in nums. You may return the answer in any order.

Example 1:

Input: nums = [10,6,5,8]
Output: [10,8]
Explanation:
- 10 is a lonely number since it appears exactly once and 9 and 11 does not appear in nums.
- 8 is a lonely number since it appears exactly once and 7 and 9 does not appear in nums.
- 5 is not a lonely number since 6 appears in nums and vice versa.
Hence, the lonely numbers in nums are [10, 8].
Note that [8, 10] may also be returned.

Example 2:

Input: nums = [1,3,5,3]
Output: [1,5]
Explanation:
- 1 is a lonely number since it appears exactly once and 0 and 2 does not appear in nums.
- 5 is a lonely number since it appears exactly once and 4 and 6 does not appear in nums.
- 3 is not a lonely number since it appears twice.
Hence, the lonely numbers in nums are [1, 5].
Note that [5, 1] may also be returned.

Constraints:

• 1 <= nums.length <= 105
• 0 <= nums[i] <= 106

Solutions (Rust)

1. Solution

use std::collections::HashMap;

impl Solution {
    pub fn find_lonely(nums: Vec<i32>) -> Vec<i32> {
        let mut is_lonely = HashMap::new();

        for &n in &nums {
            is_lonely
                .entry(n)
                .and_modify(|b| *b = false)
                .or_insert(true);
            is_lonely.insert(n + 1, false);
            is_lonely.insert(n - 1, false);
        }

        nums.into_iter().filter(|n| is_lonely[n]).collect()
    }
}