minSubArrayLen.js

// Write a function which accepts two parameters - an array of positive integers
// and a positive integer. This function should return the minimal length of a contiguous
// subarray of which the sum is greater than or equal to the integer passed. If there isn't
// one, return 0 instead.

let minSubArrayLen = (nums, sum) => {
  let total = 0
  let start = 0
  let end = 0
  let minLen = Infinity

  while (start < nums.length) {
    if (total < sum && end < nums.length) {
      total += nums[end]
      end++
    } else if (total >= sum) {
      minLen = Math.min(minLen, end - start)
      total -= nums[start]
      start++
    } else {
      break
    }
  }

  return minLen === Infinity ? 0 : minLen;
}

// This solves it in O(n) as it has 2 pointers which form a sliding window and compares the size difference.