codewars练习记录20 js

文章目录

[6 kyu] Simple Encryption #1 - Alternating Split
[6 kyu] Kebabize
[6 kyu] Decipher this!
[6 kyu] A Rule of Divisibility by 13
[6 kyu] Array Helpers

[6 kyu] Simple Encryption #1 - Alternating Split

Implement a pseudo-encryption algorithm which given a string S and an integer N concatenates all the odd-indexed characters of S with all the even-indexed characters of S, this process should be repeated N times.

Examples:

encrypt(“012345”, 1) => “135024”
encrypt(“012345”, 2) => “135024” -> “304152”
encrypt(“012345”, 3) => “135024” -> “304152” -> “012345”
encrypt(“01234”, 1) => “13024”
encrypt(“01234”, 2) => “13024” -> “32104”
encrypt(“01234”, 3) => “13024” -> “32104” -> “20314”

Together with the encryption function, you should also implement a decryption function which reverses the process.

If the string S is an empty value or the integer N is not positive, return the first argument without changes.
翻译：
实现一个伪加密算法，给定一个字符串S和一个整数N，将S的所有奇数索引字符与S的所有偶数索引字符连接起来，这个过程应该重复N次。

与加密函数一起，您还应该实现一个解密函数，该函数可以反转过程。
如果字符串S是空值或整数N不是正数，则返回第一个参数而不进行更改。
解一：

function encrypt (text, n) {if (text == null) return nullfor (let k = 0; k < n; k++) {let odd = text.split('').filter((x, i) => i % 2 != 0)let even = text.split('').filter((x, i) => i % 2 == 0)text = odd.concat(even).join('')}return text
}function decrypt (encryptedText, n) {if (!encryptedText) {return encryptedText}var char = encryptedText.split('')for (let i = 0; i < n; i++) {var odd = char.slice(0, char.length / 2)var even = char.slice(char.length / 2)char = []while (odd.length || even.length) {if (even.length) {char.push(even.shift())}if (odd.length) {char.push(odd.shift())}}}return char.join('')
}

解二：

function encrypt(text, n) {for (let i = 0; i < n; i++) {text = text && text.replace(/.(.|$)/g, '$1') + text.replace(/(.)./g, '$1') }return text
}function decrypt(text, n) {let l = text && text.length / 2 | 0for (let i = 0; i < n; i++) {text = text.slice(l).replace(/./g, (_, i) => _ + (i < l ? text[i] : ''))}return text
}

[6 kyu] Kebabize

Modify the kebabize function so that it converts a camel case string into a kebab case.

kebabize(‘camelsHaveThreeHumps’) // camels-have-three-humps
kebabize(‘camelsHave3Humps’) // camels-have-humps

翻译：
修改kebabize函数，使其将camel大小写字符串转换为kebab大小写。
解一：

function kebabize(str) {let newstr = str.replace(/[^a-zA-Z]/g, '') // 将所有非字母元素删掉for (let i = 0; i < newstr.length; i++) {if (newstr[i] >= 'A' && newstr[i] <= 'Z')newstr = newstr.replace(newstr[i], '-' + newstr[i].toLowerCase())else if (newstr[i] >= 'a' && newstr[i] <= 'z')continueelsenewstr = newstr.replace(newstr[i], '')}if (newstr[0] == '-') newstr = newstr.substring(1)return newstr
}

解二：

function kebabize(str) {return str.replace(/[^a-z]/ig, '').replace(/^[A-Z]/, c => c.toLowerCase()).replace(/[A-Z]/g, c => `-${c.toLowerCase()}`);
}

[6 kyu] Decipher this!

You are given a secret message you need to decipher. Here are the things you need to know to decipher it:
For each word:
the second and the last letter is switched (e.g. Hello becomes Holle)
the first letter is replaced by its character code (e.g. H becomes 72)
Note: there are no special characters used, only letters and spaces
Examples

decipherThis(‘72olle 103doo 100ya’); // ‘Hello good day’
decipherThis(‘82yade 115te 103o’); // ‘Ready set go’

翻译：
你会收到一条需要破译的秘密信息。以下是你需要知道的事情来破译它：
对于每个单词：
切换第二个和最后一个字母（例如Hello变成Holle）
第一个字母被其字符代码替换（例如H变为72）
注意：没有使用特殊字符，只有字母和空格
解一：

function decipherThis(str) {let brr = str.split(' ').map(x => x.replace(x.replace(/[^\d]/g, ''), String.fromCharCode(x.replace(/[^\d]/g, ''))))  //字符替换return brr.map(function (y) {  //交换位置let b = y.split('')let temp = b[1]b[1] = b[b.length - 1]b[b.length - 1] = tempreturn b.join('')}).join(' ')
};

解二：

function decipherThis(str) {return str.split(" ").map(w =>w.replace(/^\d+/, c => String.fromCharCode(c)).replace(/^(.)(.)(.*)(.)$/, "$1$4$3$2")).join(" ")
}

[6 kyu] A Rule of Divisibility by 13

From Wikipedia:

“A divisibility rule is a shorthand way of determining whether a given integer is divisible by a fixed divisor without performing the division, usually by examining its digits.”

When you divide the successive powers of 10 by 13 you get the following remainders of the integer divisions:

1, 10, 9, 12, 3, 4 because:

10 ^ 0 ->  1 (mod 13)
10 ^ 1 -> 10 (mod 13)
10 ^ 2 ->  9 (mod 13)
10 ^ 3 -> 12 (mod 13)
10 ^ 4 ->  3 (mod 13)
10 ^ 5 ->  4 (mod 13)

Then the whole pattern repeats. Hence the following method:

Multiply

the right most digit of the number with the left most number in the sequence shown above,
the second right most digit with the second left most digit of the number in the sequence.

The cycle goes on and you sum all these products. Repeat this process until the sequence of sums is stationary.

Example:

What is the remainder when 1234567 is divided by 13?

7      6     5      4     3     2     1  (digits of 1234567 from the right)
×      ×     ×      ×     ×     ×     ×  (multiplication)
1     10     9     12     3     4     1  (the repeating sequence)

Therefore following the method we get:

7×1 + 6×10 + 5×9 + 4×12 + 3×3 + 2×4 + 1×1 = 178

We repeat the process with the number 178:

8x1 + 7x10 + 1x9 = 87

and again with 87:

7x1 + 8x10 = 87

From now on the sequence is stationary (we always get 87) and the remainder of 1234567 by 13 is the same as the remainder of 87 by 13 ( i.e 9).

Task:

Call thirt the function which processes this sequence of operations on an integer n (>=0). thirt will return the stationary number.

thirt(1234567) calculates 178, then 87, then 87 and returns 87.

thirt(321) calculates 48, 48 and returns 48
（个人理解）大意就是将例数（例如：1234567）的倒序（7654321）的每一位数和数列1,10,9,12,3,4,1 （该数列由10的连续幂除以13取模则取余数所得固定的）的每一位数相乘再相加，再循环操作所得结果，直到循环前后结果相同，输出最终值
解：

function thirt(n) {var arr=[1,10,9,12,3,4]while(n>=100){var sum = nn=0for(let i=0;sum!=0;n=n+Math.floor(sum%10) * arr[i%6],sum=sum/10,i++);}return n
}

解：

function thirt(n) {const nums = [1,10,9,12,3,4]var sum = (''+n).split('').reverse().reduce((sum,v,i) => sum + v * nums[i%nums.length], 0)return sum === n ? n : thirt(sum)
}

[6 kyu] Array Helpers

This kata is designed to test your ability to extend the functionality of built-in classes. In this case, we want you to extend the built-in Array class with the following methods: square(), cube(), average(), sum(), even() and odd().

Explanation:

square() must return a copy of the array, containing all values squared
cube() must return a copy of the array, containing all values cubed
average() must return the average of all array values; on an empty array must return NaN (note: the empty array is not tested in Ruby!)
sum() must return the sum of all array values
even() must return an array of all even numbers
odd() must return an array of all odd numbers
Note: the original array must not be changed in any case!

Example

var numbers = [1, 2, 3, 4, 5];
numbers.square(); // must return [1, 4, 9, 16, 25]
numbers.cube(); // must return [1, 8, 27, 64, 125]
numbers.average(); // must return 3
numbers.sum(); // must return 15
numbers.even(); // must return [2, 4]
numbers.odd(); // must return [1, 3, 5]

翻译：
说明：
此kata旨在测试您扩展内置类功能的能力。在本例中，我们希望您使用以下方法扩展内置Array类：square（）、cube（）、average（）、sum（）、even（）和odd（）。
说明：
square（）必须返回数组的副本，其中包含所有平方值
cube（）必须返回数组的副本，其中包含所有立方值
average（）必须返回所有数组值的平均值；在空数组上必须返回NaN（注意：空数组未在Ruby中测试！）
sum（）必须返回所有数组值的总和
even（）必须返回所有偶数的数组
odd（）必须返回所有奇数的数组
注意：在任何情况下都不能更改原始数组！
解：

Object.assign(Array.prototype, {square() {return this.map(n => n * n);},cube() {return this.map(n => Math.pow(n, 3));},sum() {return this.reduce((p,n) => p + n, 0);},average() {return this.reduce((p,n) => p + n, 0) / this.length;},even() {return this.filter(n => !(n % 2));},odd() {return this.filter(n => n % 2);}
});

解：

Array.prototype.square  = function () { return this.map(function(n) { return n*n; }); }
Array.prototype.cube    = function () { return this.map(function(n) { return n*n*n; }); }
Array.prototype.average = function () { return this.sum() / this.length; }
Array.prototype.sum     = function () { return this.reduce(function(a, b) { return a + b; }, 0); }
Array.prototype.even    = function () { return this.filter(function(item) { return 0 == item % 2; }); }
Array.prototype.odd     = function () { return this.filter(function(item) { return 0 != item % 2; }); }