560. Subarray Sum Equals K

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Problem

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:

• $1<=nums.length<=2\ast {10}^4$
• -1000 <= nums[i] <= 1000
• $-{10}^7<=k<={10}^7$

Code

523. Continuous Subarray Sum

class Solution {
    public int subarraySum(int[] nums, int k) {
        int res = 0;
        int sum = 0;
        
        HashMap<Integer, Integer> map = new HashMap<>();
        map.put(0, 1);

        for (int i = 0; i < nums.length; i++) {
            sum += nums[i];
            if (map.containsKey(sum - k)) {
                res += map.get(sum - k);
            }

            map.put(sum, map.getOrDefault(sum, 0) + 1);
        }
        
        return res;
    }
}