LeetCode 560. Subarray Sum Equals K

Question

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

https://leetcode.com/problems/subarray-sum-equals-k/

• Solution1

class Solution {
    public int subarraySum(int[] nums, int k) {
        Map<Integer, Integer> map = new HashMap<>();
        int sum = 0, res = 0;
        map.put(0, 1);
        for (int num : nums){
            sum += num;
            if (map.containsKey(sum - k)) res += map.get(sum - k);
            map.put(sum, map.getOrDefault(sum, 0) + 1);
        }
        return res;
    }
}

Complexity:

Time complexity: O(n)

Space complexity: O(n)