subarray-sum-equals-k.js

/**
 * Subarray Sum Equals K
 *
 * Given an array of integers and an integer k,
 * you need to find the total number of continuous subarrays whose sum equals to k.
 *
 * Example 1:
 *
 * Input:nums = [1,1,1], k = 2
 * Output: 2
 *
 * Note:
 * The length of the array is in range [1, 20,000].
 * The range of numbers in the array is [-1000, 1000] and the range of the integer k is [-1e7, 1e7].
 */

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
const subarraySum = (nums, k) => {
  let count = 0;
  let sum = 0;

  const map = new Map();
  map.set(0, 1);

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

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

    map.set(sum, ~~map.get(sum) + 1);
  }

  return count;
};

export { subarraySum };