73 lines
1.3 KiB
Markdown
73 lines
1.3 KiB
Markdown
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---
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id: af7588ade1100bde429baf20
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title: 尋找缺失的字母
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challengeType: 5
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forumTopicId: 16023
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dashedName: missing-letters
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---
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# --description--
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在這道題目中，我們需要寫一個函數，找出傳入的字符串裏缺失的字母並返回它。
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如果所有字母都在傳入的字符串範圍內，返回 `undefined`。
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# --hints--
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`fearNotLetter("abce")` 應該返回字符串 `d`。
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```js
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assert.deepEqual(fearNotLetter('abce'), 'd');
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```
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`fearNotLetter("abcdefghjklmno")` 應返回 `i`。
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```js
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assert.deepEqual(fearNotLetter('abcdefghjklmno'), 'i');
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```
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`fearNotLetter("stvwx")` 應該返回字符串 `u`。
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```js
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assert.deepEqual(fearNotLetter('stvwx'), 'u');
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```
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`fearNotLetter("bcdf")` 應該返回字符串 `e`。
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```js
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assert.deepEqual(fearNotLetter('bcdf'), 'e');
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```
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`fearNotLetter("abcdefghijklmnopqrstuvwxyz")` 應返回 `undefined`。
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```js
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assert.isUndefined(fearNotLetter('abcdefghijklmnopqrstuvwxyz'));
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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 fearNotLetter(str) {
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return str;
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}
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fearNotLetter("abce");
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```
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# --solutions--
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```js
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function fearNotLetter (str) {
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for (var i = str.charCodeAt(0); i <= str.charCodeAt(str.length - 1); i++) {
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var letter = String.fromCharCode(i);
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if (str.indexOf(letter) === -1) {
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return letter;
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}
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}
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return undefined;
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}
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```
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