README.md

523. Continuous Subarray Sum

Given an integer array nums and an integer k, return true if nums has a good subarray or false otherwise.

A good subarray is a subarray where:

• its length is at least two, and
• the sum of the elements of the subarray is a multiple of k.

Note that:

• A subarray is a contiguous part of the array.
• An integer x is a multiple of k if there exists an integer n such that x = n * k. 0 is always a multiple of k.

Example 1:

Input: nums = [23,2,4,6,7], k = 6
Output: true
Explanation: [2, 4] is a continuous subarray of size 2 whose elements sum up to 6.

Example 2:

Input: nums = [23,2,6,4,7], k = 6
Output: true
Explanation: [23, 2, 6, 4, 7] is an continuous subarray of size 5 whose elements sum up to 42.
42 is a multiple of 6 because 42 = 7 * 6 and 7 is an integer.

Example 3:

Input: nums = [23,2,6,4,7], k = 13
Output: false

Constraints:

• 1 <= nums.length <= 105
• 0 <= nums[i] <= 109
• 0 <= sum(nums[i]) <= 231 - 1
• 1 <= k <= 231 - 1

Solutions (Rust)

1. Solution

use std::collections::HashMap;

impl Solution {
    pub fn check_subarray_sum(nums: Vec<i32>, k: i32) -> bool {
        let mut prefix_mod = 0;
        let mut mod_indices = HashMap::from([(0, -1)]);

        for i in 0..nums.len() {
            prefix_mod = (prefix_mod + nums[i]) % k;

            match mod_indices.get(&prefix_mod) {
                Some(j) if j + 1 < i as i32 => return true,
                None => {
                    mod_indices.insert(prefix_mod, i as i32);
                }
                _ => (),
            }
        }

        false
    }
}