Unique number of occurrences

Array Hash Table

78.6% acceptance

Feb 25, 2026

5543

155

Given an array of integers arr, return true if the number of occurrences of each value in the array is unique or false otherwise.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn unique_occurrences(arr: Vec<i32>) -> bool {
    use std::collections::{HashMap, HashSet};
    let mut counts: HashMap<i32, i32> = HashMap::new();
    for x in arr {
      *counts.entry(x).or_insert(0) += 1;
    }
    let vals: Vec<i32> = counts.values().cloned().collect();
    let unique: HashSet<i32> = vals.iter().cloned().collect();
    vals.len() == unique.len()
  }
}