test7.js

/* Sliding Window - maxSubarraySum
Given an array of integers and a number, write a function called maxSubarraySum, which finds the 
maximum sum of a subarray with the length of the number passed to the function.

Note that a subarray must consist of consecutive elements from the original array. 
In the first example below, [100, 200, 300] is a subarray of the original array, but [100, 300] is not.

maxSubarraySum([100,200,300,400], 2) // 700
maxSubarraySum([1,4,2,10,23,3,1,0,20], 4)  // 39
maxSubarraySum([-3,4,0,-2,6,-1], 2) // 5
maxSubarraySum([3,-2,7,-4,1,-1,4,-2,1],2) // 5
maxSubarraySum([2,3], 3) // null */

// 1차 솔루션
const maxSubarraySum = (arr, num) => {
  if (arr.length < num) return null;
  let max = 0;
  let temp = 0;
  for (i = 0; i < num; i++) {
    max += arr[i];
  }
  temp = max;
  for (i = num; i < arr.length; i++) {
    temp = temp + arr[i] - arr[i - num];
    max = Math.max(max, temp);
  }
  return max;
};

console.log(maxSubarraySum([1, 4, 2, 10, 23, 3, 1, 0, 20], 4));