36 lines
765 B
Markdown
36 lines
765 B
Markdown
importance: 5
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---
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# Sum all numbers till the given one
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Write a function `sumTo(n)` that calculates the sum of numbers `1 + 2 + ... + n`.
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For instance:
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```js no-beautify
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sumTo(1) = 1
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sumTo(2) = 2 + 1 = 3
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sumTo(3) = 3 + 2 + 1 = 6
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sumTo(4) = 4 + 3 + 2 + 1 = 10
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...
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sumTo(100) = 100 + 99 + ... + 2 + 1 = 5050
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```
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Make 3 solution variants:
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1. Using a for loop.
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2. Using a recursion, cause `sumTo(n) = n + sumTo(n-1)` for `n > 1`.
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3. Using the [arithmetic progression](https://en.wikipedia.org/wiki/Arithmetic_progression) formula.
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An example of the result:
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```js
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function sumTo(n) { /*... your code ... */ }
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alert( sumTo(100) ); // 5050
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```
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P.S. Which solution variant is the fastest? The slowest? Why?
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P.P.S. Can we use recursion to count `sumTo(100000)`?
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