2.3 KiB
2.3 KiB
id | challengeType | title |
---|---|---|
5900f3851000cf542c50fe98 | 5 | Problem 25: 1000-digit Fibonacci number |
Description
Fn = Fn−1 + Fn−2, where F1 = 1 and F2 = 1.
Hence the first 12 terms will be:
F1 = 1
F2 = 1
F3 = 2
F4 = 3
F5 = 5
F6 = 8
F7 = 13
F8 = 21
F9 = 34
F10 = 55
F11 = 89
F12 = 144
Instructions
Tests
tests:
- text: <code>digitFibonacci(5)</code> should return 21.
testString: 'assert.strictEqual(digitFibonacci(5), 21, "<code>digitFibonacci(5)</code> should return 21.");'
- text: <code>digitFibonacci(10)</code> should return 45.
testString: 'assert.strictEqual(digitFibonacci(10), 45, "<code>digitFibonacci(10)</code> should return 45.");'
- text: <code>digitFibonacci(15)</code> should return 69.
testString: 'assert.strictEqual(digitFibonacci(15), 69, "<code>digitFibonacci(15)</code> should return 69.");'
- text: <code>digitFibonacci(20)</code> should return 93.
testString: 'assert.strictEqual(digitFibonacci(20), 93, "<code>digitFibonacci(20)</code> should return 93.");'
Challenge Seed
function digitFibonacci(n) {
// Good luck!
return n;
}
digitFibonacci(20);
Solution
const digitFibonacci = (n) => {
const digits = (num) => {
return num.toString().length;
};
let f1 = 1;
let f2 = 1;
let index = 3;
while (true) {
let fn = f1 + f2;
if (digits(fn) === n) return index;
[f1, f2] = [f2, fn];
index++;
}
};