## 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`

## Rust Solution

``````struct Solution;

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

impl Solution {
fn unique_occurrences(arr: Vec<i32>) -> bool {
let mut hm: HashMap<i32, i32> = HashMap::new();
for x in arr {
*hm.entry(x).or_default() += 1;
}
let mut hs = HashSet::new();
for x in hm.values() {
if !hs.insert(x) {
return false;
}
}
true
}
}

#[test]
fn test() {
let arr = vec![1, 2, 2, 1, 1, 3];
assert_eq!(Solution::unique_occurrences(arr), true);
let arr = vec![1, 2];
assert_eq!(Solution::unique_occurrences(arr), false);
let arr = vec![-3, 0, 1, -3, 1, 1, 1, -3, 10, 0];
assert_eq!(Solution::unique_occurrences(arr), true);
}
``````

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