560. Subarray Sum Equals K

Given an array of integers `nums` and an integer `k`, return the total number of continuous subarrays whose sum equals to `k`.

Example 1:

```Input: nums = [1,1,1], k = 2
Output: 2
```

Example 2:

```Input: nums = [1,2,3], k = 3
Output: 2
```

Constraints:

• `1 <= nums.length <= 2 * 104`
• `-1000 <= nums[i] <= 1000`
• `-107 <= k <= 107`

Rust Solution

``````struct Solution;

use std::collections::HashMap;

impl Solution {
fn subarray_sum(nums: Vec<i32>, k: i32) -> i32 {
let mut sum = 0;
let mut hm: HashMap<i32, i32> = HashMap::new();
let mut res = 0;
hm.insert(0, 1);
for x in nums {
sum += x;
res += hm.get(&(sum - k)).unwrap_or(&0);
*hm.entry(sum).or_default() += 1;
}
res
}
}

#[test]
fn test() {
let nums = vec![1, 1, 1];
let k = 2;
assert_eq!(Solution::subarray_sum(nums, k), 2);
let nums = vec![0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
let k = 0;
assert_eq!(Solution::subarray_sum(nums, k), 55);
}
``````

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