LeetCode 560. Subarray Sum Equals K

Problem Statement

use std::collections::HashMap;

impl Solution {
    pub fn subarray_sum(nums: Vec<i32>, k: i32) -> i32 {
        let (mut ans, mut sum) = (0, 0);
        let mut map = HashMap::new();
        map.insert(0, 1);
        for i in 0..nums.len() {
            sum += nums[i];
            map.entry(sum - k).or_insert(0);
            ans += map[&(sum - k)];
            map.entry(sum).or_insert(0);
            *map.get_mut(&sum).unwrap() += 1;
        }
        return ans;
    }
}