## 961. N-Repeated Element in Size 2N Array

In a array `A` of size `2N`, there are `N+1` unique elements, and exactly one of these elements is repeated `N` times.

Return the element repeated `N` times.

Example 1:

```Input: [1,2,3,3]
Output: 3
```

Example 2:

```Input: [2,1,2,5,3,2]
Output: 2
```

Example 3:

```Input: [5,1,5,2,5,3,5,4]
Output: 5
```

Note:

• `4 <= A.length <= 10000`
• `0 <= A[i] < 10000`
• `A.length` is even

## Rust Solution

``````struct Solution;

use std::collections::HashSet;

impl Solution {
fn repeated_n_times(a: Vec<i32>) -> i32 {
let mut hs: HashSet<i32> = HashSet::new();
for x in a {
if !hs.insert(x) {
return x;
}
}
unreachable!()
}
}

#[test]
fn test() {
let a = vec![1, 2, 3, 3];
assert_eq!(Solution::repeated_n_times(a), 3);
let a = vec![2, 1, 2, 5, 3, 2];
assert_eq!(Solution::repeated_n_times(a), 2);
let a = vec![5, 1, 5, 2, 5, 3, 5, 4];
assert_eq!(Solution::repeated_n_times(a), 5);
}
``````

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