How to sum specific elements in an array?

Question

I am trying to manipulate an array. For each operation, I need to add a value to each the array element between two given indices, inclusive. Here is one example:

0 1 100  // From index 0 to 1, add 100
1 4 100  // From index 1 to 4, add 100
2 3 100  // From index 2 to 3, add 100

// Expected Result:
[100, 200, 200, 200, 100]

// Explanation:
[100, 100] // After the first update.
[100, 200, 100, 100, 100] // After the second update.
[100, 200, 200, 200, 100] // After the third update.

And this was as far as I got:

function arrayManipulation(n, queries) {
  let newArr = [];
  for (let i = 0; i < queries.length; i++) {
    let indexIni = queries[i][0];
    let indexEnd = queries[i][1];
    let indexSum = queries[i][2];

    for (indexIni; indexIni < indexEnd; indexIni++) {
      console.log(indexIni, indexEnd, indexSum);
      newArr.splice(indexIni, 0, indexSum);
    }
  }
  console.log(newArr);
}

let n1 = 5;
let queries1 = [
  [0, 1, 100],
  [1, 4, 100],
  [2, 3, 100]
];
arrayManipulation(n1, queries1);

What I was trying to do was work on top of the second parameter of splice() so that I could somehow add it up to the number I was going to input.

The way I'm trying, is it possible? Or is there a simpler method?

Simpler method? Why can't you just traverse from indexIni to indexEnd and add indexSum to the elements? — PG1
– PG1, Commented Jun 17, 2021 at 0:06

DecPK · Accepted Answer · 2021-06-17 00:07:40Z

3

1) loop should go upto

indexIni <= indexEnd

2) Iterating from the start and checking if any number is present on that particular index or not. If it does then add the indexSum else set the value as indexSum.

function arrayManipulation(n, queries) {
  let newArr = [];
  for (let i = 0; i < queries.length; i++) {
    let [indexIni, indexEnd, indexSum] = queries[i];

    for (indexIni; indexIni <= indexEnd; indexIni++) {
      if (newArr[indexIni]) {
        newArr[indexIni] += indexSum;
      } else {
        newArr[indexIni] = indexSum;
      }
    }
  }
  console.log(newArr);
}

let n1 = 5;
let queries1 = [
  [0, 1, 100],
  [1, 4, 100],
  [2, 3, 100],
];
arrayManipulation(n1, queries1);

answered Jun 17, 2021 at 0:07

DecPK

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6 Comments

ARNON Over a year ago

Pretty solution! Exactly what I need. Thanks!!

PG1 Over a year ago

You probably need to initialize the array as well because if some of the indexes are missing from the operations then those elements in the array won't be defined

DecPK Over a year ago

@ParagGangil That's why I've used the if (newArr[indexIni]) condition.

DecPK Over a year ago

@ParagGangil I agree there will be empty items, but OP doesn't say about that so why to worry...

DecPK Over a year ago

We have to first find the highest number and then fill it will zero instead I would prefer to filter the final result as newArr = newArr.filter((n) => n);. This will remove all the empty item.

|

Siva Kondapi Venkata · Accepted Answer · 2021-06-17 05:16:40Z

2

Using forEach and Array.from

function arrayManipulation(data) {
  const res = [];
  data.forEach(([start, end, value]) => {
    Array.from({ length: end - start + 1 }, (_, i) => start + i).forEach(
      (index) => (res[index] = (res[index] ?? 0) + value)
    );
  });
  return res;
}

const data = [
  [0, 1, 100],
  [1, 4, 100],
  [2, 3, 100],
];

console.log(arrayManipulation(data));

answered Jun 17, 2021 at 5:16

Siva Kondapi Venkata

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