use std::collections::HashMap;
fn find_element_that_appears_once_in_array(arr: &[i32]) -> i32 {
let mut map = HashMap::new();
for x in arr {
*map.entry(x).or_insert(0) += 1;
}
for (key, value) in map.iter() {
if *value == 1 {
return **key;
}
}
-1
}
fn main() {
let arr = [3, 5, 5, 2, 7, 3, 2, 8, 8, 3, 2, 5, 8];
println!("{}", find_element_that_appears_once_in_array(&arr));
}
/*
run:
7
*/