minSubArrayLen.js

// Task: 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 or which the sum is greater than or equal to the integer passed to the function. If there isn't one, return 0 instead

const 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++;
    }
    // if current window adds up to at least the sum given then
    // we can shrink the window
    else if (total >= sum) {
      minLen = Math.min(minLen, end - start);
      total -= nums[start];
      start++;
    }
    // current total less than required total but we reach the end, need this or else we'll be in an infinite loop
    else {
      break;
    }
  }
  return minLen === Infinity ? 0 : minLen;
};