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---
id: 594810f028c0303b75339ad3
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title: Vector dot product
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challengeType: 5
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forumTopicId: 302343
2021-01-13 02:31:00 +00:00
dashedName: vector-dot-product
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---
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# --description--
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A vector is defined as having three dimensions as being represented by an ordered collection of three numbers: (X, Y, Z).
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# --instructions--
Write a function that takes any numbers of vectors (arrays) as input and computes their dot product. Your function should return `null` on invalid inputs such as vectors of different lengths.
# --hints--
dotProduct should be a function.
```js
assert.equal(typeof dotProduct, 'function');
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```
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dotProduct() should return null.
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```js
assert.equal(dotProduct(), null);
```
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dotProduct(\[[1], [1]]) should return 1.
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```js
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assert.equal(dotProduct([1], [1]), 1);
```
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dotProduct(\[[1], [1, 2]]) should return null.
```js
assert.equal(dotProduct([1], [1, 2]), null);
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```
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dotProduct([1, 3, -5], [4, -2, -1]) should return 3.
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```js
assert.equal(dotProduct([1, 3, -5], [4, -2, -1]), 3);
```
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`dotProduct(...nVectors)` should return 156000.
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```js
assert.equal(
dotProduct(
[0, 1, 2, 3, 4],
[0, 2, 4, 6, 8],
[0, 3, 6, 9, 12],
[0, 4, 8, 12, 16],
[0, 5, 10, 15, 20]
),
156000
);
```
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# --seed--
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## --seed-contents--
```js
function dotProduct(...vectors) {
}
```
# --solutions--
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```js
function dotProduct(...vectors) {
if (!vectors || !vectors.length) {
return null;
}
if (!vectors[0] || !vectors[0].length) {
return null;
}
const vectorLen = vectors[0].length;
const numVectors = vectors.length;
// If all vectors not same length, return null
for (let i = 0; i < numVectors ; i + + ) {
if (vectors[i].length !== vectorLen) {
return null; // return undefined
}
}
let prod = 0;
let sum = 0;
let j = vectorLen;
let i = numVectors;
// Sum terms
while (j--) {
i = numVectors;
prod = 1;
while (i--) {
prod *= vectors[i][j];
}
sum += prod;
}
return sum;
}
```