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use std::collections::HashMap;
struct Solution;
impl Solution {
pub fn number_of_arithmetic_slices(nums: Vec<i32>) -> i32 {
let (n, mut ans) = (nums.len(), 0);
let mut map: Vec<HashMap<i64, i32>> = Vec::with_capacity(n);
for i in 1..n {
for j in 0..i {
let diff: i64 = nums[i] as i64 - nums[j] as i64;
let count = match map.len() {
0 => 0,
_ => *map[j].get(&diff).unwrap_or(&0)
};
if map.len() < i + 1 {
let n = i - map.len() + 1;
map.extend(vec![HashMap::new(); n]);
}
map[i].entry(diff).and_modify(|x| *x += count + 1).or_insert(count + 1);
ans += count;
}
}
ans
}
}
fn main() {
let nums = vec![2,4,6,8,10];
print!("{}", Solution::number_of_arithmetic_slices(nums));
}
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