ee1e8abd87
* feat(tools): add seed/solution restore script * chore(curriculum): remove empty sections' markers * chore(curriculum): add seed + solution to Chinese * chore: remove old formatter * fix: update getChallenges parse translated challenges separately, without reference to the source * chore(curriculum): add dashedName to English * chore(curriculum): add dashedName to Chinese * refactor: remove unused challenge property 'name' * fix: relax dashedName requirement * fix: stray tag Remove stray `pre` tag from challenge file. Signed-off-by: nhcarrigan <nhcarrigan@gmail.com> Co-authored-by: nhcarrigan <nhcarrigan@gmail.com>
172 lines
1.6 KiB
Markdown
172 lines
1.6 KiB
Markdown
---
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id: 5900f3851000cf542c50fe98
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title: 问题25：1000位斐波纳契数
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challengeType: 5
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videoUrl: ''
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dashedName: problem-25-1000-digit-fibonacci-number
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---
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# --description--
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Fibonacci序列由递归关系定义：
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F
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<sub>n</sub>
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= F
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<sub>n-1</sub>
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- F
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<sub>n-2</sub>
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，其中F
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<sub>1</sub>
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= 1且F
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<sub>2</sub>
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= 1。
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因此，前12个学期将是：
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F
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<sub>1</sub>
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= 1
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F
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<sub>2</sub>
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= 1
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F
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<sub>3</sub>
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= 2
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F
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<sub>4</sub>
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= 3
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F
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<sub>5</sub>
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= 5
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F
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<sub>6</sub>
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= 8
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F
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<sub>7</sub>
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= 13
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F
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<sub>8</sub>
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= 21
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F
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<sub>9</sub>
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= 34
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F
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<sub>10</sub>
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= 55
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F
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<sub>11</sub>
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= 89
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F
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<sub>12</sub>
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= 144
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第12个学期F
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<sub>12</sub>
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是第一个包含三位数的术语。 Fibonacci序列中包含`n个`数字的第一项的索引是多少？
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# --hints--
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`digitFibonacci(5)`应该返回21。
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```js
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assert.strictEqual(digitFibonacci(5), 21);
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```
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`digitFibonacci(10)`应该返回45。
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```js
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assert.strictEqual(digitFibonacci(10), 45);
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```
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`digitFibonacci(15)`应该返回69。
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```js
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assert.strictEqual(digitFibonacci(15), 69);
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```
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`digitFibonacci(20)`应该返回93。
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```js
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assert.strictEqual(digitFibonacci(20), 93);
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```
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# --seed--
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## --seed-contents--
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```js
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function digitFibonacci(n) {
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return n;
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}
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digitFibonacci(20);
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```
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# --solutions--
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```js
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const digitFibonacci = (n) => {
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const digits = (num) => {
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return num.toString().length;
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};
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let f1 = 1;
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let f2 = 1;
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let index = 3;
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while (true) {
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let fn = f1 + f2;
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if (digits(fn) === n) return index;
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[f1, f2] = [f2, fn];
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index++;
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}
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};
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```
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