2021-06-15 07:49:18 +00:00
---
id: 5900f3a11000cf542c50feb4
2021-08-25 16:12:11 +00:00
title: 'Problema 53: Seleção de combinações'
2021-06-15 07:49:18 +00:00
challengeType: 5
forumTopicId: 302164
dashedName: problem-53-combinatoric-selections
---
# --description--
2021-08-25 16:12:11 +00:00
Existem exatamente dez maneiras de selecionar um número de 3 dígitos a partir de um número de 5 dígitos, 12345:
2021-06-15 07:49:18 +00:00
2021-08-25 16:12:11 +00:00
< div style = 'text-align: center;' > 123, 124, 125, 134, 135, 145, 234, 235, 245 e 345< / div >
2021-06-15 07:49:18 +00:00
2021-08-25 16:12:11 +00:00
Na combinatória, usamos a notação $\\displaystyle \\binom 5 3 = 10$
2021-06-15 07:49:18 +00:00
2021-08-25 16:12:11 +00:00
No geral, $\\displaystyle \\binom n r = \\dfrac{n!}{r!(n-r)!}$, onde $r \\le n$, $n! = n \\times (n-1) \\times ... \\times 3 \\times 2 \\times 1$, e $0! = 1$.
2021-06-15 07:49:18 +00:00
2021-08-25 16:12:11 +00:00
É só depois de $n = 23$ que um valor excede um milhão: $\\displaystyle \\binom {23} {10} = 1144066$.
2021-06-15 07:49:18 +00:00
2021-08-25 16:12:11 +00:00
Quantos valores de $\\displaystyle \\binom n r$ para $1 \\le n \\le 100$, não necessariamente distintos, são maiores que um milhão?
2021-06-15 07:49:18 +00:00
# --hints--
2021-08-25 16:12:11 +00:00
`combinatoricSelections(1000)` deve retornar um número.
2021-06-15 07:49:18 +00:00
```js
assert(typeof combinatoricSelections(1000) === 'number');
```
2021-08-25 16:12:11 +00:00
`combinatoricSelections(1000)` deve retornar 4626.
2021-06-15 07:49:18 +00:00
```js
assert.strictEqual(combinatoricSelections(1000), 4626);
```
2021-08-25 16:12:11 +00:00
`combinatoricSelections(10000)` deve retornar 4431.
2021-06-15 07:49:18 +00:00
```js
assert.strictEqual(combinatoricSelections(10000), 4431);
```
2021-08-25 16:12:11 +00:00
`combinatoricSelections(100000)` deve retornar 4255.
2021-06-15 07:49:18 +00:00
```js
assert.strictEqual(combinatoricSelections(100000), 4255);
```
2021-08-25 16:12:11 +00:00
`combinatoricSelections(1000000)` deve retornar 4075.
2021-06-15 07:49:18 +00:00
```js
assert.strictEqual(combinatoricSelections(1000000), 4075);
```
# --seed--
## --seed-contents--
```js
function combinatoricSelections(limit) {
return 1;
}
combinatoricSelections(1000000);
```
# --solutions--
```js
function combinatoricSelections(limit) {
const factorial = n =>
Array.apply(null, { length: n })
.map((_, i) => i + 1)
.reduce((p, c) => p * c, 1);
let result = 0;
const nMax = 100;
for (let n = 1; n < = nMax; n++) {
for (let r = 0; r < = n; r++) {
if (factorial(n) / (factorial(r) * factorial(n - r)) >= limit)
result++;
}
}
return result;
}
```