560. Subarray Sum Equals K

Given an array of integers nums and an integer k, return the total number of 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 * 10^4
• -1000 <= nums[i] <= 1000
• -10^7 <= k <= 10^7

Approach

Solution

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
var subarraySum = function(nums, k) {
  const map = new Map();
  map.set(0, 1);

  let sum = 0;
  let count = 0;

  for (let n of nums){
    sum += n;

    if(map.has(sum - k)){
      count += map.get(sum - k);
    }

    map.set(sum, (map.get(sum) || 0) + 1);
  }
  return count
};

Explanation