daily CodeWars

每天都在codewars做题，刷题。

记录一下。。

CodeWars

Javascript filter - 1

function searchNames(logins){return logins.filter(function(login){return /_$/.test(login[0])});
}

The range() function

function range(start, end, step) {
step = step===undefined?1:step;
if(end===undefined){end = start;start = 0;
}
if(end==0){return [];
}
var res = [start];
if(step!=0){while(start+step<end){start += step;res.push(start);}
}else{for(var i=2; i<end;i++){res.push(start);}
}
return res;
}

Convert a Number to a String!

function numberToString(num){return ''+num;
}

Who likes it?

function likes(names) {
var res='',len = names.length;
switch(len){case 0:res = 'no one likes this';break;case 1:res = names[0] + " likes this";break;case 2:res = names[0]+" and "+ names[1]+ " like this";break;case 3:res = names[0]+", "+ names[1]+" and "+names[2] + " like this";break;default:res = names[0]+", "+ names[1]+" and "+(names.length-2) +" others like this";break;
}
return res;
}

Naughty or Nice?

function getNiceNames(people){
return people.filter(function(per){return per.wasNice;
}).map(function(e){return e.name});
}
function getNaughtyNames(people){
return people.filter(function(per){return !per.wasNice;
}).map(function(e){return e.name});
}

return a sorted list of objects

function sortList (sortBy, list) {
return list.sort(function(a, b){return parseInt(b[sortBy])-parseInt(a[sortBy])});
}

Find the Remainder

function remainder(a, b){
return Math.max(a,b)%Math.min(a,b);
}

Building Strings From a Hash

function solution(pairs){var re="";for(var i in pairs){re += i+" = "+pairs[i]+','}return re.substring(0,re.length-1);
}

Array.diff

//原来还可以用indexOf 来判断数组元素是否存在
function array_diff(a, b) {
return a.filter(function(e){return b.indexOf(e)==-1});
}

No oddities here

function noOdds( values ){
return values.filter(function(e){return e%2==0;});
}

Flatten

//我的渣做法
var flatten = function (array){
var res = [],len = array.length;
for(var i=0;i<len;i++){var ar = array[i];if(ar instanceof Array){for(var j=0;j<ar.length;j++){res.push(ar[j]);}}else{res.push(ar);}
}
return res;
}
//优雅做法
var flatten = function (array){
return [].concat.apply([],array);
}

Mr.Freeze

// mark the MrFreeze object instance as frozen
Object.freeze(MrFreeze);

Pluck

function pluck(objs, name) {
return objs.map(function(obj){return obj[name];
});
}

Reverse words

//原来reverse是Array的方法,String是没有的
function reverseWords(str) {return str.split(" ").map(function(a){return a.split('').reverse().join('');}).join(" ");
}

Get key/value pairs as arrays

function keysAndValues(data){
var keys=[],values=[],res = [];
for(var key in data){keys.push(key);values.push(data[key]);
}
res.push(keys);
res.push(values);
return res;
}
//优雅写法
function keysAndValues(data){return [Object.keys(data)].push(Object.keys(data).map(function(e){return data[e]}));
}

SantaClausable Interface

//踩坑点:要判断是否为function
function isSantaClausable(obj) {return (typeof obj.sayHoHoHo =='function')&&(typeof obj.distributeGifts == 'function')&&(typeof obj.goDownTheChimney == 'function');
}
//优雅写法
function isSantaClausable(obj) {return ['sayHoHoHo','distributeGifts','goDownTheChimney'].every(function(m){return typeof obj[m]=='function'});
}

Disemvowel Trolls

function disemvowel(str) {
return str.split('').map(function(e){if(['e','i','o','a','u','A','O','E','I','U'].indexOf(e)==-1){return e;}
}).join('');
}
//best practice
function disemvowel(str) {
return str.replace(/[aeiou]/gi, '');
}

Summing a number's digits

function sumDigits(number) {var sum = 0;
(number<0?(-number)+'':number+'').split('').forEach(function(e){sum+=parseInt(e)});
return sum;
}

Number Of Occurrences

Array.prototype.numberOfOccurrences = function() {
if(arguments.length<1){return 0;
}
var times = 0,arg = arguments[0];
this.forEach(function(e){if(e===arg){//argument不能乱用，只能用局部变量暂存times++;}
});
return times;
}
//best practice
Array.prototype.numberOfOccurrences = function(search){return this.filter(function(num){return search===num}).length;
};

Count characters in your string

function count (string) {  var res = {};var str = string.split('').forEach(function(e){res[e] = res[e]?res[e]+1:1;});return res;
}

Reversed Strings

function solution(str){
return str.split('').reverse().join('');
}

Sentence Smash

function smash (words) {
  "use strict";return words.join(' ');
};

Sort the Gift Code

function sortGiftCode(code){
return code.split('').sort().join('');
}

Remove anchor from URL

function removeUrlAnchor(url){
return url.split('#')[0];
}

Basic Training: Add item to an Array
```
websites.push('codewars');
```

Anything to integer

function toInteger(n) {
var num = Number(n)+'';
var t= num.split('\.')[0];
if(num=='Infinity'||num=='NaN')return 0;
return Number(t);
}

Is Integer Array ?

function isIntArray(arr) {
return arr instanceof Array?arr.every(function(e){return e!=null &&typeof e != 'string'&&!isNaN(e)&&(e+'').indexOf('.')==-1}):false;
}

Return substring instance count

function solution(fullText, searchText){
return fullText.split(searchText).length-1;
}

Sort arrays - 1

sortme = function( names ){
return names.sort();
}

Sort arrays - 2

sortme = function( names ){return names.sort(function(a,b){return a.toLowerCase().localeCompare(b.toLowerCase())})
}

Functional Addition

function add(n) {
return function(){return arguments[0]+n;
}
}

Function 2 - squaring an argument
```
function square(e){
return e*e;
}
```

Singleton Pattern

var Singleton = function(){
if(Singleton._instance)return Singleton._instance;
if(!this instanceof Singleton)return new Singleton();
Singleton._instance = this;
};

Sentences with Functions

function Adam() {return arguments[0]?'Adam '+arguments[0]:'Adam.'}
function has() {return 'has '+arguments[0]}
function a() {return 'a '+arguments[0]}
function dog() {return arguments[0]?'dog '+arguments[0]:'dog.'}
function The() {return 'The '+arguments[0]}
function name() {return 'name '+arguments[0]}
function of() {return 'of '+arguments[0]}
function the() {return 'the '+arguments[0]}
function is() {return 'is '+arguments[0]}
function also() {return 'also '+arguments[0]}

Elapsed Seconds

function elapsedSeconds(startDate, endDate){
return (Date.parse(endDate)-Date.parse(startDate))/1000;
}

Trim a String

String.prototype.trim = function() {
return this.replace(/^\s*/g,'').replace(/\s*$/g,'');
};

Square(n) Sum

function squareSum(numbers){return numbers.map(function(e){return e*e}).reduce(function(e1,e2){return e1+e2});
}

The Coupon Code

function checkCoupon(enteredCode, correctCode, currentDate, expirationDate){
if(enteredCode===correctCode){return new Date(currentDate)<=new Date(expirationDate);
}
return false;
}

Operator overload ?

var Foo = function(value) {
this.val = value;
}
Foo.prototype.valueOf = function(){
return this.val;
}

JavaScript class-like objects

function Animal(name, type){
this.name = name;
this.type = type;
this.toString = function(){return this.name+' is a '+this.type;
}
}

Anagram Detection

var isAnagram = function(test, original) {var tl = original.toLowerCase();
return test.length==original.length&&test.toLowerCase().split('').every(function(e){return tl.indexOf(e)>-1})
};

esreveR gnirtS

String.prototype.reverse = function(){
return this.split('').reverse().join('');
}

Basic JS - Calculating averages

var Calculator = {
average: function() {
return arguments.length?Array.prototype.reduce.call(arguments, function(a,b){return a+b})/arguments.length:0;
}
};

Numerology

/**
* Your solution
* @date JS Date object
**/
function solution(date){
var sum = (date.getDate()+date.getMonth()+1+date.getFullYear());
return splitsum(splitsum(sum));
}
function splitsum(i){
return Number((''+i).split('').reduce(function(a,b){return parseInt(a)+parseInt(b)}));
}

The Vowel Code

function encode(string){
return string.replace(/a/g,1).replace(/e/g,2).replace(/i/g,3).replace(/o/g,4).replace(/u/,5);
}
//turn numbers back into vowels
function decode(string){
return string.replace(/1/g,'a').replace(/2/g,'e').replace(/3/g,'i').replace(/4/g,'o').replace(/5/,'u');
}

Number-like counter

function Counter(){
this.val=0;
this.valueOf =function(){return this.val;}
}
Counter.prototype.incr = function() {
return ++this.val;
}

Name Array Capping

function capMe(names) {
return names.map(function(e){return e.substr(0,1).toUpperCase()+e.substr(1).toLowerCase();
});
}

Multiplication table

multiplicationTable = function(size) {
var arr = [];
for(var i=0;i<size;i++){arr.push(i+1);
}
return arr.map(function(e){var r = [];for(var j =1;j<size+1;j++){r.push(e*j);}return r;
});
}

Basic JS - Building a calculator

var Calculator = {};
Calculator.add = function(a,b){return a+b}
Calculator.subtract = function(a,b){return a-b}
Calculator.multiply = function(a,b){return a*b}
Calculator.divide = function(a,b){return b?a/b:false}

Milk and Cookies for Santa

function timeForMilkAndCookies(date){
return date.getMonth()==11&&date.getDate()==24;
}

Cylon Evolution

function Cylon(model){
this.model = model;
this.attack = function(){return 'Destroy all humans!';
};
}
function HumanSkin(model){
this.model = model;
this.attack = function(){return 'Destroy all humans!';
};
this.infiltrate = function(){return 'Infiltrate the colonies';
};
}
HumanSkin.prototype = new Cylon();

Javascript filter - 2

function roomMates( rooms, floor ){
return rooms.filter(function(e,i){return e&&Math.floor(i/6)==floor-1});
}

Array Helpers

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

Simple elevator

function goto(level,button){
if(typeof level != 'number'|| level<0||level>3||!/[0-3]/.test(button))return 0;
return parseInt(button)-level;
}

Use reduce() to calculate the sum of the values in an array

function sum(array) {
return array.reduce(function(a,b){return a+b});
}

Return the Missing Element

function getMissingElement(superImportantArray){
return 45-superImportantArray.reduce(function(a, b){return a+b;
});
}

The reject() function

function reject(array, iterator) {
return array.filter(function(e){return !iterator(e)})
}

Say "Hello World" JS Style

var say = function(string1) {
return function(string2){return string1 + ' '+string2;
}
}

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