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# 8 kyu
### [Grasshopper - Summation](https://www.codewars.com/kata/55d24f55d7dd296eb9000030)
:::spoiler 解法
``` javascript=
let summation = function (num) {
let sum = 0;
for(let i = 1; i<=num; i++){
sum+=i;
}
return sum;
}
```
:::
### [Reversed Strings](https://www.codewars.com/kata/5168bb5dfe9a00b126000018)
:::spoiler 解法
``` javascript=
function solution(str){
return str.split("").reverse().join("");
}
```
```javascript=
let str = "abcdefg";
str = str.split("");
console.log(str); // ['a', 'b', 'c', 'd', 'e', 'f', 'g']
str = str.reverse();
console.log(str); // ['g', 'f', 'e', 'd', 'c', 'b', 'a']
str = str.join("");
console.log(str); // gfedcba
// str = str.join(" + ");
// console.log(str); // g + f + e + d + c + b + a
```
:::
### [Count by X](https://www.codewars.com/kata/5513795bd3fafb56c200049e)
:::spoiler 解法
``` javascript=
function countBy(x, n) {
let z = [];
for(let i = 1; i<=n ; i++){
let pushNum = x * i;
z.push(pushNum);
}
return z;
}
```
:::
### [Beginner - Reduce but Grow](https://www.codewars.com/kata/57f780909f7e8e3183000078)
:::spoiler 解法
``` javascript=
function grow(x){
let result = 1;
x.forEach(item=>{
result *= item;
})
return result;
}
// const grow=x=> x.reduce((a,b) => a*b);
```
:::
### [Convert boolean values to strings 'Yes' or 'No'.](https://www.codewars.com/kata/53369039d7ab3ac506000467)
:::spoiler 解法
``` javascript=
function boolToWord( bool ){
return bool ? "Yes" : "No";
}
```
:::
### [Will there be enough space?](https://www.codewars.com/kata/5875b200d520904a04000003)
:::spoiler 解法
``` javascript=
function enough(cap, on, wait) {
let empty = cap - on - wait;
return empty >= 0 ? 0 : Math.abs(empty)
}
// function enough(cap, on, wait) {
// return Math.max(wait + on - cap, 0);
// }
```
:::
### [Abbreviate a Two Word Name](https://www.codewars.com/kata/57eadb7ecd143f4c9c0000a3)*
- 知識點：[Array.prototype.map()](https://www.codewars.com/kata/57eadb7ecd143f4c9c0000a3)
:::spoiler 解法
- 該題傳入的值也會有單字開頭是小寫的情況
``` javascript=
function abbrevName(name){
return name.split(" ").map((c)=> c[0].toUpperCase()).join(".");
}
```
:::
### [Sum without highest and lowest number](https://www.codewars.com/kata/576b93db1129fcf2200001e6)***
- 知識點：!!轉布林、null型別、[Array.prototype.reduce()](https://developer.mozilla.org/zh-TW/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce)、Math.min
:::spoiler 解法
- 注意測試值包含 null ，null 為 object，所以只能是兩個等號
``` javascript=
function sumArray(array) {
if (array == null || array.length <= 2) {
return 0;
}
array.sort((a, b) => {
return a - b;
});
array = array.slice(1, array.length - 1);
return array.reduce((a, c) => a + c);
// function sumArray(array) {
// return Array.isArray(array) && array.length > 1
// ? array.reduce((s, n) => s + n, 0) - Math.min(...array) - Math.max(...array)
// : 0
// }
}
```
- !!轉為布林，單個!結果會相反
```javascript=
function sumArray(array) {
return !!array;
}
console.log(sumArray(null)); // false
console.log(sumArray([])); // true
console.log(sumArray([-6, 20, -1, 10, -12])); // true
```
:::
### [Beginner Series #1 School Paperwork](https://www.codewars.com/kata/55f9b48403f6b87a7c0000bd)*
- 知識點：
:::spoiler 解法
``` javascript=
function paperwork(n, m) {
return n > 0 && m > 0 ? n * m : 0;
}
```
:::
### [Sum Arrays](https://www.codewars.com/kata/53dc54212259ed3d4f00071c)*
- 知識點：Array.prototype.reduce()
:::spoiler 解法
- 注意傳入 [] 要回傳 0 ，需要給初始值
``` javascript=
function sum (numbers) {
"use strict";
return numbers.reduce((a,c)=>a+c,0);
};
```
:::
### [Convert a Number to a String!](https://www.codewars.com/kata/5265326f5fda8eb1160004c8)**
- 知識點：數字轉字串的各種方法
:::spoiler 解法
``` javascript=
function numberToString(num) {
return num.toString();
}
function numberToString(num) {
// Return a string of the number here!
return String(num);
}
function numberToString(num) {
return ''+num;
}
const numberToString = num => `${num}`;
```
- 此程式碼旨在執行toString()（對於整數）的操作，但不使用內建函數。
```javascript=
function numberToString(num) {
//create a new empty string in which the result will be written
var str = '';
//Check, whether the number is positive or negative. The multiplier 1 or -1 will be saved for later
const mult = num < 0 ? -1 : 1;
//Take the absolut value of num. Could also be done with Math.abs
num *= mult;
//Loop, which will run as often as num has digits
do {
//Take the least significant digit of num (num % 10), add 48 and get the associated ascii character. The number 0 has the ascii value of 48, 1 = 49... 9 = 57.
//Then prepend that character to the string.
str = String.fromCharCode(num % 10 + 48) + str;
//Remove the least significant digit from num. (Divide by ten, then round down)
num = ~~(num / 10);
} while (num > 0);
//If the input number was negative, prepend a -.
if(mult < 0) str = "-" + str;
return str;
}
```
:::
### [Sentence Smash](https://www.codewars.com/kata/53dc23c68a0c93699800041d)*
- 知識點：Array.prototype.join()
:::spoiler 解法
```javascript=
function smash (words) {
return words.join(" ");
};
```
:::
### [Calculate average](https://www.codewars.com/kata/57a2013acf1fa5bfc4000921)****
- 知識點：Array.prototype.reduce()
:::spoiler 解法
- 要用`array.length === 0`來檢查是否為空陣列，而非`array === []`，會報錯，不能使用===運算符來比較兩個陣列是否相等
``` javascript=
function findAverage(array) {
if (array.length == 0) {
return 0;
} else {
return array.reduce((a, c) => a + c) / array.length;
}
}
console.log(findAverage([]));
```
:::
### [Even or Odd](https://www.codewars.com/kata/53da3dbb4a5168369a0000fe)*
- 知識點：%
:::spoiler 解法
``` javascript=
function evenOrOdd(number) {
return number % 2 === 0 ? "Even" : "Odd"
}
```
:::
### [Basic Mathematical Operations](https://www.codewars.com/kata/57356c55867b9b7a60000bd7)**
- 知識點：switch
:::spoiler 解法
``` javascript=
function basicOp(operation, value1, value2)
{
switch (operation) {
case "+":
return value1 + value2;
case "-":
return value1 - value2;
case "*":
return value1 * value2;
case "/":
return value1 / value2;
}
}
```
:::
### [Thinkful - Logic Drills: Traffic light](https://www.codewars.com/kata/58649884a1659ed6cb000072)*
- 知識點：用陣列處理、三元運算子、物件解法
:::spoiler 解法
``` javascript=
function updateLight(current) {
const trafficLight = ["green", "yellow", "red"];
return current === "red"
? trafficLight[0]
: trafficLight[trafficLight.indexOf(current) + 1];
}
console.log(updateLight("green"));
console.log(updateLight("yellow"));
console.log(updateLight("red"));
```
```javascript=
// 物件解法
const updateLight = current => ({
green: 'yellow',
yellow: 'red',
red: 'green',
})[current]
```
:::
### [Keep Hydrated!](https://www.codewars.com/kata/582cb0224e56e068d800003c)***
- 知識點：Math.floor()
:::spoiler 解法
``` javascript=
function litres(time) {
return Math.floor(time * 0.5);
}
```
:::
### [Remove String Spaces](https://www.codewars.com/kata/57eae20f5500ad98e50002c5)*
- 知識點：正則、[String.prototype.replace()](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/String/replace)
:::spoiler 解法
``` javascript=
function noSpace(x){
return x.replace(/\s/g,"")
}
```
```javascript=
function noSpace(x){return x.split(' ').join('')}
```
:::
### [The Feast of Many Beasts](https://www.codewars.com/kata/5aa736a455f906981800360d)*
- 知識點：[String.prototype.slice()](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/String/slice)為負值的話是從尾部開始算、startsWith、endsWith
:::spoiler 解法
``` javascript=
function feast(beast, dish) {
return beast[0] === dish[0] && beast[beast.length - 1] === dish[dish.length - 1]
}
```
```javascript=
function feast(beast, dish) {
return beast[0]===dish[0] && beast.slice(-1)===dish.slice(-1);
}
```
```javascript=
function feast(beast, dish) {
return dish.startsWith(beast[0]) && dish.endsWith(beast[beast.length-1])
}
```
:::
### [String cleaning](https://www.codewars.com/kata/57e1e61ba396b3727c000251)**
- 知識點：正則，\d 為匹配數字
:::spoiler 解法
``` javascript=
function stringClean(s){
return s.replace(/\d/g, "")
}
```
:::
### [Is the string uppercase?](https://www.codewars.com/kata/56cd44e1aa4ac7879200010b)***
- 知識點：String.prototype.match() 若沒匹配到會回傳 null
:::spoiler 解法
``` javascript=
String.prototype.isUpperCase = function() {
const regex = /[a-z]/g;
return this.match(regex) === null;
}
```
:::
### [Stringy Strings](https://www.codewars.com/kata/563b74ddd19a3ad462000054)**
- 知識點：String.prototype.repeat()、String.prototype.padStart()
:::spoiler 解法
``` javascript=
function stringy(size) {
const pair = "10";
const pairs = pair.repeat(Math.floor(size / 2));
return size % 2 === 1 ? pairs + 1 : pairs;
}
```
```javascript=
const stringy = size => "10".repeat(size).slice(0,size);
```
```javascript=
const stringy = x => ''.padStart(x,'10');
```
:::
### [Training JS #8: Conditional statement--switch](https://www.codewars.com/kata/572059afc2f4612825000d8a)**
- 知識點：switch 多 case 執行相同程式碼
:::spoiler 解法
``` javascript=
function howManydays(month) {
var days;
switch (month) {
case 2:
days = 28;
break;
case 4:
case 6:
case 9:
case 11:
days = 30;
break;
default:
days = 31;
}
return days;
}
howManydays(12);
```
:::
### [Will you make it?](https://www.codewars.com/kata/5861d28f124b35723e00005e)*
- 知識點：
:::spoiler 解法
``` javascript=
const zeroFuel = (distanceToPump, mpg, fuelLeft) => {
return distanceToPump <= mpg * fuelLeft;
};
```
:::
### [Counting sheep...](https://www.codewars.com/kata/54edbc7200b811e956000556)*
- 知識點：
:::spoiler 解法
``` javascript=
function countSheeps(sheep) {
let sheepCount = 0;
sheep.forEach(e => e === true ? sheepCount++ : sheepCount)
return sheepCount
}
```
:::
### [I love you, a little , a lot, passionately ... not at all](https://www.codewars.com/kata/57f24e6a18e9fad8eb000296)***
- 知識點：調換陣列順序
:::spoiler 解法
``` javascript=
function howMuchILoveYou(nbPetals) {
const phrases = [
"I love you",
"a little",
"a lot",
"passionately",
"madly",
"not at all",
];
return phrases[nbPetals % 6 === 0 ? phrases.length - 1 : (nbPetals % 6) - 1];
}
```
```javascript=
function howMuchILoveYou(nbPetals) {
const phrases = [
"not at all",
"I love you",
"a little",
"a lot",
"passionately",
"madly",
];
return phrases[nbPetals % 6];
}
```
:::
### [Rock Paper Scissors!](https://www.codewars.com/kata/5672a98bdbdd995fad00000f)**
- 知識點：物件寫法
:::spoiler 解法
``` javascript=
const rps = (p1, p2) => {
if (p1 === p2) return "Draw!";
if (p1 === "scissors") {
if (p2 === "rock") {
return "Player 2 won!";
} else if (p2 === "paper") {
return "Player 1 won!";
}
}
if (p1 === "rock") {
if (p2 === "scissors") {
return "Player 1 won!";
} else if (p2 === "paper") {
return "Player 2 won!";
}
}
if (p1 === "paper") {
if (p2 === "scissors") {
return "Player 2 won!";
} else if (p2 === "rock") {
return "Player 1 won!";
}
}
};
```
```javascript=
const rps = (p1, p2) => {
if (p1 === p2) return "Draw!";
var rules = {rock: "scissors", paper: "rock", scissors: "paper"};
if (p2 === rules[p1]) {
return "Player 1 won!";
}
else {
return "Player 2 won!";
}
};
```
:::
### [Return Negative](https://www.codewars.com/kata/55685cd7ad70877c23000102)*
- 知識點：
:::spoiler 解法
``` javascript=
function makeNegative(num) {
return num < 0 ? num : -num;
}
```
:::
### [Correct the mistakes of the character recognition software](https://www.codewars.com/kata/577bd026df78c19bca0002c0)***
- 知識點：
:::spoiler 解法
``` javascript=
function correct(string) {
const arr = string.split("");
arr.forEach((e, i) => {
switch (e) {
case "5":
arr[i] = "S";
break;
case "0":
arr[i] = "O";
break;
case "1":
arr[i] = "I";
break;
}
});
return arr.join("");
}
correct("51NGAP0RE");
```
```javascript=
correct = s => s.replace(/0/g,'O').replace(/1/g,'I').replace(/5/g,'S')
```
```javascript=
const corrections = {
'5': 'S',
'0': 'O',
'1': 'I',
};
const correct = string => (
string.replace(/[501]/g, character => corrections[character])
);
```
:::
### [Count Odd Numbers below n](https://www.codewars.com/kata/59342039eb450e39970000a6)**
- 知識點：
:::spoiler 解法
``` javascript=
function oddCount(n){
return n%2 === 1 ? (n-1)/2 : n/2
}
```
```javascript=
const oddCount = n => Math.floor(n/2) ;
```
:::
### [Find Maximum and Minimum Values of a List](https://www.codewars.com/kata/577a98a6ae28071780000989)*
- 知識點：
:::spoiler 解法
``` javascript=
var min = function(list){
return Math.min(...list);
}
var max = function(list){
return Math.max(...list);
}
```
:::
### [Count of positives / sum of negatives](https://www.codewars.com/kata/576bb71bbbcf0951d5000044)**
- 知識點：空陣列 [] 是真值
:::spoiler 解法
``` javascript=
function countPositivesSumNegatives(input) {
if (!input || input.length === 0) return [];
const arr = [];
arr[0] = input.filter((e) => e > 0).length;
arr[1] = input.filter((e) => e < 0).reduce((a, c) => a + c, 0);
return arr;
}
countPositivesSumNegatives([
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, -11, -12, -13, -14, -15,
]);
```
:::
### [To square(root) or not to square(root)](https://www.codewars.com/kata/57f6ad55cca6e045d2000627)**
- 知識點：
:::spoiler 解法
``` javascript=
function squareOrSquareRoot(array) {
return array.map((e) =>
Number.isInteger(Math.sqrt(e)) ? Math.sqrt(e) : Math.pow(e, 2)
);
}
console.log(squareOrSquareRoot([4, 3, 9, 7, 2, 1]));
```
:::
### [ASCII Total](https://www.codewars.com/kata/572b6b2772a38bc1e700007a)*
- 知識點：
:::spoiler 解法
``` javascript=
function uniTotal (string) {
return string.split("").reduce((a,c)=> a+ c.charCodeAt(0),0);
}
```
:::
### [Flick Switch](https://www.codewars.com/kata/64fbfe2618692c2018ebbddb)**
- 知識點：
:::spoiler 解法
``` javascript=
function flickSwitch(arr){
let state = true;
return arr.map(e=>{
if(e === "flick"){
state = !state;
return state;
}else{
return state;
}
})
}
```
:::
### [Gravity Flip](https://www.codewars.com/kata/5f70c883e10f9e0001c89673)**
- 知識點：
:::spoiler 解法
``` javascript=
const flip=(d, a)=>{
switch(d){
case "R":
a.sort((a,b)=> a-b);
break;
case "L":
a.sort((a,b)=> b-a);
break;
}
return a
}
```
```javascript=
const flip = (d, a) => a.sort((x, y) => d === 'R' ? x - y : y - x);
```
:::
### [FIXME: Replace all dots](https://www.codewars.com/kata/596c6eb85b0f515834000049)**
- 知識點：
:::spoiler 解法
``` javascript=
var replaceDots = function(str) {
return str.replace(/\./g, '-');
}
```
:::
### [Add Length](https://www.codewars.com/kata/559d2284b5bb6799e9000047)*
- 知識點：
:::spoiler 解法
``` javascript=
function addLength(str) {
const arr = str.split(" ");
return arr.map((e) => e + " " + e.length);
}
```
:::
### [String Templates - Bug Fixing #5](https://www.codewars.com/kata/55c90cad4b0fe31a7200001f)**
- 知識點：
:::spoiler 解法
``` javascript=
function buildString(...template){
return `I like ${template.join(', ')}!`;
}
```
:::
### [Who is going to pay for the wall?](https://www.codewars.com/kata/58bf9bd943fadb2a980000a7)**
- 知識點：
:::spoiler 解法
``` javascript=
function whoIsPaying(name){
if(name.length<=2) return [name];
return [name,name[0]+name[1]];
}
```
:::
### [Removing Elements](https://www.codewars.com/kata/5769b3802ae6f8e4890009d2)*
- 知識點：
:::spoiler 解法
``` javascript=
function removeEveryOther(arr){
const resultArr =[]
for(let i = 0; i < arr.length; i+=2){
resultArr.push(arr[i]);
}
return resultArr;
}
```
```javascript=
function removeEveryOther(arr){
return arr.filter(function(elem, index) {
return index % 2 === 0;
});
}
```
:::
### [Chuck Norris VII - True or False? (Beginner)](https://www.codewars.com/kata/570669d8cb7293a2d1001473)*
- 知識點：其他網友解法頗有趣XDD
:::spoiler 解法
``` javascript=
function ifChuckSaysSo(){
return !true;
}
```
:::
### [Merge two sorted arrays into one](https://www.codewars.com/kata/5899642f6e1b25935d000161)**
- 知識點：Set
:::spoiler 解法
``` javascript=
function mergeArrays(arr1, arr2) {
const arr = [];
arr1.forEach((e) => arr.push(e));
arr2.forEach((e) => arr.push(e));
arr.sort((a, b) => a - b);
const result = new Set(arr);
return [...result];
}
```
```javascript=
function mergeArrays(arr1, arr2) {
return Array.from(new Set(arr1.concat(arr2).sort((a,b) => (a-b))));
}
```
:::
### [title]()**
- 知識點：
:::spoiler 解法
``` javascript=
```
:::
{"description":":::","title":"Codewars 8kyu","contributors":"[{\"id\":\"65ef09e4-76a5-4ffa-8afd-4e2465c6240e\",\"add\":20883,\"del\":4180}]"}