struct Solution;
impl Solution {
fn subarrays_div_by_k(a: Vec<i32>, k: i32) -> i32 {
let n = k as usize;
let mut count: Vec<i32> = vec![0; n];
let mut sum = 0;
let mut res = 0;
count[0] = 1;
for x in a {
sum = (sum + x % k + k) % k;
res += count[sum as usize];
count[sum as usize] += 1;
}
res
}
}
#[test]
fn test() {
let a = vec![4, 5, 0, -2, -3, 1];
let k = 5;
let res = 7;
assert_eq!(Solution::subarrays_div_by_k(a, k), res);
}