200 lines
9.6 KiB
Markdown
200 lines
9.6 KiB
Markdown
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---
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title: Find the Symmetric Difference
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localeTitle: 找到对称差异
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---
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![:triangular_flag_on_post:](https://forum.freecodecamp.com/images/emoji/emoji_one/triangular_flag_on_post.png?v=3 ":triangular_flag_on_post:")如果卡住,请记得使用[**`Read-Search-Ask`**](https://forum.freecodecamp.org/t/how-to-get-help-when-you-are-stuck/) 。尝试配对程序![:busts_in_silhouette:](https://forum.freecodecamp.com/images/emoji/emoji_one/busts_in_silhouette.png?v=3 ":busts_in_silhouette:")并编写自己的代码![:pencil:](https://forum.freecodecamp.com/images/emoji/emoji_one/pencil.png?v=3 ":铅笔:")
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### ![:checkered_flag:](https://forum.freecodecamp.com/images/emoji/emoji_one/checkered_flag.png?v=3 ":checkered_flag:")问题说明:
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两组的对称差异(通常用Δ表示)是在两组中的任一组中的元素集,但在两者中都不是。
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例如, `sym([1, 2, 3], [5, 2, 1, 4])`应该产生`[3, 4, 5]` 。
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根据上述定义,三组_A_ , _B_和_C的_对称差异可表示为`(A Δ B) Δ C`
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#### 相关链接
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* [对称差异 - 维基百科](https://en.wikipedia.org/wiki/Symmetric_difference)
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* [对称差异 - YouTube](https://www.youtube.com/watch?v=PxffSUQRkG4)
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[](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce)
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[## ![:speech_balloon:](https://forum.freecodecamp.com/images/emoji/emoji_one/speech_balloon.png?v=3 ":speech_balloon:")提示:1
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_arguments_对象是类似_Array_的对象,只继承`Array.length`属性。因此,请考虑将其转换为实际的_数组_ 。
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> _现在尝试解决问题_
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## ![:speech_balloon:](https://forum.freecodecamp.com/images/emoji/emoji_one/speech_balloon.png?v=3 ":speech_balloon:")提示:2
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Deem编写一个辅助函数,在每次调用时返回两个数组的对称差异,而不是试图同时区分所有集合。
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> _现在尝试解决问题_
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## ![:speech_balloon:](https://forum.freecodecamp.com/images/emoji/emoji_one/speech_balloon.png?v=3 ":speech_balloon:")提示:3
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对创建的arguments数组应用辅助函数,递归地逐对减少元素,以形成预期的输出。
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**注意** 在_奇数个集合_的情况下,对称差异将包括在所有给定集合中存在的相同元素。例如;
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```
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A = {1, 2, 3}
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B = {2, 3, 4}
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C = {3, 4, 5}
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(A ⋂ B) ⋂ C = {1, 4} &Intersection {3, 4, 5}
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A ⋂ B = {1, 3, 5}
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```
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> _现在尝试解决问题_
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## 扰流警报!
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![:warning:](//discourse-user-assets.s3.amazonaws.com/original/2X/2/2d6c412a50797771301e7ceabd554cef4edcd74d.gif ":警告:")
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**提前解决!**
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## ![:beginner:](https://forum.freecodecamp.com/images/emoji/emoji_one/beginner.png?v=3 ":初学者:")基本代码解决方案
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```javascript
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function sym() {
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var args = [];
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for (var i = 0; i < arguments.length; i++) {
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args.push(arguments[i]);
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}
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function symDiff(arrayOne, arrayTwo) {
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var result = [];
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arrayOne.forEach(function(item) {
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if (arrayTwo.indexOf(item) < 0 && result.indexOf(item) < 0) {
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result.push(item);
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}
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});
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arrayTwo.forEach(function(item) {
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if (arrayOne.indexOf(item) < 0 && result.indexOf(item) < 0) {
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result.push(item);
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}
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});
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return result;
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}
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// Apply reduce method to args array, using the symDiff function
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return args.reduce(symDiff);
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}
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```](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce)
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[![:rocket:](https://forum.freecodecamp.com/images/emoji/emoji_one/rocket.png?v=3 ":火箭:")](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce) [运行代码](https://repl.it/C4II/0)
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### 代码说明:
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* `push()`用于将_arguments_对象分解为数组_args_ 。
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* `symDiff`函数查找两个集合之间的对称差异。它用作_args上_调用的`reduce()`方法的回调函数。
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* `arrayOne.forEach()`将元素推送到_结果_ ,这些元素仅存在于_arrayOne中_ ,并且还不是_结果_的一部分。
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* `arrayTwo.forEach()`将元素推送到_结果中_ ,这些元素仅存在于_arrayTwo中_ ,并且还不是_结果_的一部分。
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* 返回_结果_ ,即对称差异。此解决方案适用于任意数量的集合。
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#### 相关链接
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* [JavaScript for](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/statements/for)
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* [JavaScript Array.length](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/length)
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* [JavaScript Array.prototype.push()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push)
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* [JavaScript Array.prototype.forEach()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach)
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* [JavaScript Array.prototype.indexOf()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf)
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## ![:sunflower:](https://forum.freecodecamp.com/images/emoji/emoji_one/sunflower.png?v=3 ":向日葵:")中级代码解决方案:
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```javascript
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function sym() {
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// Convert the argument object into a proper array
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var args = Array.prototype.slice.call(arguments);
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// Return the symmetric difference of 2 arrays
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var getDiff = function(arr1, arr2) {
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// Returns items in arr1 that don't exist in arr2
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function filterFunction(arr1, arr2) {
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return arr1.filter(function(item) {
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return arr2.indexOf(item) === -1;
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});
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}
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// Run filter function on each array against the other
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return filterFunction(arr1, arr2)
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.concat(filterFunction(arr2, arr1));
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};
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// Reduce all arguments getting the difference of them
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var summary = args.reduce(getDiff, []);
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// Run filter function to get the unique values
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var unique = summary.filter(function(elem, index, self) {
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return index === self.indexOf(elem);
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});
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return unique;
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}
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// test here
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sym([1, 2, 3], [5, 2, 1, 4]);
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```
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![:rocket:](https://forum.freecodecamp.com/images/emoji/emoji_one/rocket.png?v=3 ":火箭:") [运行代码](https://repl.it/CLoc/0)
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### 代码说明:
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* `slice()`方法用于将_arguments_对象分解为数组_args_ 。
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* `getDiff`函数查找两个集合_arr1_和_arr2_之间的对称差异。它用作_args上_调用的`reduce()`方法的回调函数。
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* 第一个`filterFunction()`返回_arr1_中_arr2中_不存在的元素。
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* 下一个`filterFunction()`在每个数组`filterFunction()`对于另一个运行,以检查第一次检查唯一性的反转并连接它。
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* _摘要_包含减少的参数。
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* `filter()`用在_总结_只保留唯一值,并返回_唯一的_ 。
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#### 相关链接
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* [JavaScript Array.prototype.slice()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice)
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* [JavaScript Array.prototype.filter()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter)
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* [JavaScript Array.prototype.concat()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat)
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## ![:rotating_light:](https://forum.freecodecamp.com/images/emoji/emoji_one/rotating_light.png?v=3 ":rotating_light:")高级代码解决方案
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```javascript
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function sym() {
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let argv = Array.from(arguments).reduce(diffArray);
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return argv.filter((element, index, array) => index === array.indexOf(element));//remove duplicates
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}
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function diffArray(arr1, arr2) {
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return arr1
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.filter(element => !arr2.includes(element))
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.concat(arr2.filter(element => !arr1.includes(element)));
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}
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// test here
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sym([1, 2, 3], [5, 2, 1, 4]);
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```
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![:rocket:](https://forum.freecodecamp.com/images/emoji/emoji_one/rocket.png?v=3 ":火箭:") [运行代码](https://repl.it/@ashenm/Symmetric-Difference)
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### 代码说明:
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* 主函数_sym()_从_参数_创建一个数组,并使用辅助函数_diffArray()_将其元素_简化_为单个数组。
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* 函数_diffArray()_通过挑选参数化数组中的唯一元素来返回两个数组的对称差异; _arr1_和_arr2_ 。
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#### 相关链接
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* [JavaScript Array.from()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from)
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* [JavaScript Array.prototype.filter()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter)
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## ![:clipboard:](https://forum.freecodecamp.com/images/emoji/emoji_one/clipboard.png?v=3 ":剪贴板:")捐款说明:
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* ![:warning:](https://forum.freecodecamp.com/images/emoji/emoji_one/warning.png?v=3 ":警告:") **请勿**添加与任何现有解决方案类似的解决方案。如果您认为它**_相似但更好_** ,那么尝试合并(或替换)现有的类似解决方案。
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* 添加解决方案的说明。
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* 将解决方案分为以下类别之一 - **基本** , **中级**和**高级** 。 ![:traffic_light:](https://forum.freecodecamp.com/images/emoji/emoji_one/traffic_light.png?v=3 ":红绿灯:")
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* 如果您添加了任何**相关的主要内容,**请仅添加您的用户名。 ( ![:warning:](https://forum.freecodecamp.com/images/emoji/emoji_one/warning.png?v=3 ":警告:") **_不要_** _删除任何现有的用户名_ )
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> 看到![:point_right:](https://forum.freecodecamp.com/images/emoji/emoji_one/point_right.png?v=3 ":point_right:") [**`Wiki Challenge Solution Template`**](http://forum.freecodecamp.com/t/algorithm-article-template/14272)供参考。
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