CodeWar 代码练习

CodeWar-kyu.js

/**
Implement pluck, which takes an array of objects and a property name, 
and returns an array containing the named property of each object.

For example:

pluck([{a:1}, {a:2}], 'a') // -> [1,2]
If an object is missing the property, you should just leave it as undefined in the output array.
*/
// mine
function pluck(objs, name) {
  var rst = [];
  for (var i = 0; i < objs.length; i++)  
    rst.push(objs[i][name]);
  return rst;
}
// wow~
function pluck(objs, name) {
  return objs.map(function(obj) { return obj[name] });
}

/**
 * There is an object/class already created called MrFreeze. 
 * Mark this object as frozen so that no other changes can be made to it.
 * 
 * -----------------------
 * 参考 : Object.freeze 函数 
 *        阻止修改现有属性的特性和值，并阻止添加新属性。
 * link: http://msdn.microsoft.com/zh-cn/library/ff806186(v=vs.94).aspx
 **/
// mine 

// wow~
Object.freeze(MrFreeze)
// and this
function deepFreeze (o) {
  var prop, propKey;
  Object.freeze(o); // First freeze the object.
  for (propKey in o) {
    prop = o[propKey];
    if (!o.hasOwnProperty(propKey) || !(typeof prop === "object") || Object.isFrozen(prop)) {
      // If the object is on the prototype, not an object, or is already frozen, 
      // skip it. Note that this might leave an unfrozen reference somewhere in the
      // object if there is an already frozen object containing an unfrozen object.
      continue;
    }
 
    deepFreeze(prop); // Recursively call deepFreeze.
  }
}
deepFreeze(MrFreeze);

/**
 * A friend of yours is developing an application for a hotel. 
 * You should write a function that returns all names of the people on a given floor. 
 * Every floor has 6 rooms, and all rooms are numbered in a consecutive way.
 * The function has the following signature:
 *    function roomMates( rooms, floor ){}
 * 
 * The argument room holds all clients in an array, where the index (starts at 0) 
 * corresponds to the room-number (starts at 1) and holds the name of the client.
 *    [ "foo", "bar" ]
 * 
 * Means that foo (index 0) stays in room #1 and bar (index 1) in room #2.
 * Empty rooms shouldn't be returned, so he can directly count the number of 
 * occupied rooms by looking at the length of the array.
 * 
 * --------------------------------------
 * 参考: Array.prototype.filter()
 *       返回数组中的满足回调函数中指定的条件的元素。
 * link:https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter
 * */
// mine
function roomMates ( rooms, floor ) {
  return rooms.filter (function (room,index) {
    return room != "" &&
     (Math.floor(index / 6) + 1) == floor;
  })
}
// wow~
function roomMates( rooms, floor  {
  // slice这里倒是简单，NB的在于 filter 里的 return v ，为空 的话 自动返回false了
  return rooms.slice((floor - 1) * 6, floor * 6).filter(function(v) { return v; });
}

/**
 * We need a function that can transform a number into a string.
 * What ways of achieving this do you know?
 * Examples:
 *   numberToString(123); // returns '123';
 *   numberToString(999); // returns '999';
 * */
// mine
function numberToString(num) {
  return num + "";
}
// wow~
function numberToString(num) {
  return num.toString();
}

/**
 * Trolls are attacking your comment section!
 * A common way to deal with this situation is to remove all of the vowels from the trolls' comments,
 * neutralizing the threat.
 * Your task is to write a function that takes a string and return a new string with all vowels removed.
 * For example, the string "This website is for losers LOL!" would become "Ths wbst s fr lsrs LL!".
 * */
// mine
function disemvowel(str) {
  return str.replace(/[aeiouAEIOU]/g,"");
}
// wow~
function disemvowel(str) {
  // 开了 i 选项忽略大小写
  return str.replace(/[aeiou]/gi, '');
}

/**
 * You'll be passed an array of objects - 
 * you must sort them in descending order based on the value of an arbitrarily specified property.
 * For example, when sorted by a, this:
 *   [
 *    {a: 1, b: 3},
 *    {a: 3, b: 2},
 *    {a: 2, b: 40},
 *    {a: 4, b: 12}
 *   ]
 * should return:
 *   [
 *    {a: 4, b: 12},
 *    {a: 3, b: 2},
 *    {a: 2, b: 40},
 *   {a: 1, b: 3}
 *   ]
 * */
// mine
function sortList (sortBy, list) {
  return list.sort(function (a,b) {
    if (a[sortBy] == b[sortBy]) return 0;
    else if (a[sortBy] < b[sortBy]) return 1;
    else return -1;
  })
}
// wow~
function sortList (sortBy, list) {
  return list.sort(function(a, b) { return b[sortBy] - a[sortBy]; });
}

/**
 * Description:
 * You probably know the "like" system from Facebook and other pages. 
 * People can "like" blog posts, pictures or other items. 
 * We want to create the text that should be displayed next to such an item.
 * Implement a function likes(), which must take in input array, containing the names of people who like an item. 
 * It must return the display text as shown in the examples:
 * 
 *     likes([]); // must return "no one likes this"
 *     likes(['Peter']); // must return "Peter likes this"
 *     likes(['Jacob', 'Alex']); // must return "Jacob and Alex like this"
 *     likes(['Max', 'John', 'Mark']); // must return "Max, John and Mark like this"
 *     likes(['Alex', 'Jacob', 'Mark', 'Max']); // must return "Alex, Jacob and 2 others like this"
 * */
// mine
// 最笨的实现，使用了 4个if语句判断
// wow~
function likes(names) {
  names[0] = names[0] || "no one";
  if (names.length > 3) names[2] = names.length-2 + " others";
  return names.slice(0,3).join(", ").replace(/(.*), /, "$1 and ") + " like" + (names.length<2 ? "s" : "") + " this";
}
// and this
function likes(names) {
  names = names || [];
  // 简单的等值判断 使用 switch 可以简化很多
  switch(names.length){
    case 0: return 'no one likes this'; break;
    case 1: return names[0] + ' likes this'; break;
    case 2: return names[0] + ' and ' + names[1] + ' like this'; break;
    case 3: return names[0] + ', ' + names[1] + ' and ' + names[2] + ' like this'; break;
    default: return names[0] + ', ' + names[1] + ' and ' + (names.length - 2) + ' others like this';
  }
}