README.md

1207. Unique Number of Occurrences

Given an array of integers arr, write a function that returns true if and only if the number of occurrences of each value in the array is unique.

Example 1:

Input: arr = [1,2,2,1,1,3]
Output: true
Explanation: The value 1 has 3 occurrences, 2 has 2 and 3 has 1. No two values have the same number of occurrences.

Example 2:

Input: arr = [1,2]
Output: false

Example 3:

Input: arr = [-3,0,1,-3,1,1,1,-3,10,0]
Output: true

Constraints:

• 1 <= arr.length <= 1000
• -1000 <= arr[i] <= 1000

Solutions (Rust)

1. HashMap & Set

use std::collections::HashMap;
use std::collections::HashSet;

impl Solution {
    pub fn unique_occurrences(arr: Vec<i32>) -> bool {
        let mut map = HashMap::new();
        for n in arr {
            *map.entry(n).or_insert(0) += 1;
        }

        let set: HashSet<_> = map.values().collect();

        set.len() == map.len()
    }
}

2. Sort

impl Solution {
    pub fn unique_occurrences(arr: Vec<i32>) -> bool {
        let mut arr = arr;
        arr.sort_unstable();

        let mut times = [false; 1001];
        let mut i = 0;
        let mut j = 1;
        while i < arr.len() {
            while j < arr.len() && arr[i] == arr[j] {
                j += 1;
            }
            if times[j - i] {
                return false;
            }
            times[j - i] = true;
            i = j;
        }

        true
    }
}