## 523. Continuous Subarray Sum

Given a list of non-negative numbers and a target integer k, write a function to check if the array has a continuous subarray of size at least 2 that sums up to a multiple of k, that is, sums up to n*k where n is also an integer.

Example 1:

```Input: [23, 2, 4, 6, 7],  k=6
Output: True
Explanation: Because [2, 4] is a continuous subarray of size 2 and sums up to 6.
```

Example 2:

```Input: [23, 2, 6, 4, 7],  k=6
Output: True
Explanation: Because [23, 2, 6, 4, 7] is an continuous subarray of size 5 and sums up to 42.
```

Constraints:

• The length of the array won't exceed 10,000.
• You may assume the sum of all the numbers is in the range of a signed 32-bit integer.

## Rust Solution

``````struct Solution;
use std::collections::HashSet;

impl Solution {
fn check_subarray_sum(nums: Vec<i32>, k: i32) -> bool {
let n = nums.len();
let mut sum = 0;
let mut pre = 0;
let mut hs: HashSet<i32> = HashSet::new();
for i in 0..n {
sum += nums[i];
let cur = if k == 0 { sum } else { sum % k };
if hs.contains(&cur) {
return true;
}
hs.insert(pre);
pre = cur;
}
false
}
}

#[test]
fn test() {
let nums = vec![23, 2, 4, 6, 7];
let k = 6;
let res = true;
assert_eq!(Solution::check_subarray_sum(nums, k), res);
let nums = vec![23, 2, 6, 4, 7];
let k = 6;
let res = true;
assert_eq!(Solution::check_subarray_sum(nums, k), res);
let nums = vec![23, 2, 6, 4, 7];
let k = 0;
let res = false;
assert_eq!(Solution::check_subarray_sum(nums, k), res);
let nums = vec![0, 0];
let k = -1;
let res = true;
assert_eq!(Solution::check_subarray_sum(nums, k), res);
}
``````

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