At what index does the sum reach a certain value-CodePudding

I have an array of numbers and some limit.

const a = [1,2,1,3,4,1,2];
const limit = 5;

What's the most javascripty way of reducing this array to the index such that the sum from the beginning to the index would exceed the limit?

I've done

function findIndex(nums, limit) {
      let s = 0;
      for (let [index, num] of nums.entries()) {
        s  = num;
        if (s >= limit) {
          return index;
        }
      }
      return nums.length;
    }

findIndex([1,2,1,3,4,1,2], 5)
3

Is there a more neat way of doing this using reduce or something else?

CodePudding user response：

As you're after the index, you could look at using the array method .findIndex(). The below code adds to sum for each item in arr, and then checks whether the new accumulate sum value is greater than or equal to the limit. If it is, the callback for findIndex will return true, giving you the index. If the callback function to findIndex doesn't find any values, it will result in -1, which you can then check before you return to see if you need to return the array length or the actual index:

const findIndex = (arr, limit) => {
  let sum = 0;
  const idx = arr.findIndex((num, idx) => (sum =num) >= limit);
  return idx > 0 ? idx : arr.length; 
}

console.log(findIndex([1,2,1,3,4,1,2], 5));

CodePudding user response：

Since you need the

1) index upto which the sum is greater or equal to limit

2) You want to return early as soon as the sum exceeds limit

then you should go for old school for loop. There is no need to accumulate the index and value using nums.entries()

function findIndex(nums, limit) {
  let sum = 0;
  for (let i = 0; i < nums.length;   i) {
    sum  = nums[i];
    if (sum >= limit) return i;
  }
  // Return something explicitely to 
  // indicate that sum can't exceeds limit.
  // You may return -1 if you like
}
console.log(findIndex([1, 2, 1, 3, 4, 1, 2], 5));