CodeWars 学习记录（二）

Posted at 2020-01-03 JavaScript JavaScript

CamelCase Method

Write simple .camelCase method (camel_case function in PHP, CamelCase in C# or camelCase in Java) for strings. All words must have their first letter capitalized without spaces.

For instance:

1 2	"hello case".camelCase() => HelloCase "camel case word".camelCase() => CamelCaseWord

解法

我自己的解法

String.prototype.camelCase = function () {
  let uw = this.replace(/\b\w+\b/g, function (word) {
    return word.substring(0, 1).toUpperCase() + word.substring(1);
  });
  return uw.replace(" ", "");
};

看到的更加巧妙的解法

String.prototype.camelCase = function () {
  const capitalize = (word) => {
    return word.slice(0, 1).toUpperCase() + word.slice(1);
  };

  return this
    .split(" ")
    .map(capitalize)
    .join("");
};

Format a string of names like ‘Bart, Lisa & Maggie’

Given: an array containing hashes of names.

Return: a string formatted as a list of names separated by commas except for the last two names, which should be separated by an ampersand.

Example:

list([{name: "Bart"}, {name: "Lisa"}, {name: "Maggie"}])
// returns "Bart, Lisa & Maggie"

list([{name: "Bart"}, {name: "Lisa"}])
// returns "Bart & Lisa"

list([{name: "Bart"}])
// returns "Bart"

list([])
// returns ""

解法

function list(names) {
  return names.formatName();
}

Array.prototype.formatName = function () {
  let result = "";
  this.forEach((item, index) => {
    if (index === 0) {
      result = item.name;
    } else if (index === this.length - 1) {
      result = `${result} & ${item.name}`;
    } else {
      result = `${result}, ${item.name}`;
    }
  });

  return result;
};

scramble

Complete the function scramble(str1, str2) that returns true if a portion of str1 characters can be rearranged to match str2, otherwise returns false.

Notes:

Only lower case letters will be used (a-z).
Performance needs to be considered.

Examples:

1
2
3

scramble("rkqodlw", "world") ==> true
scramble("cedewaraaossoqqyt", "codewars") ==> true
scramble("katas", "steak") ==> false

我的解法

function scramble(str1, str2) {
  var count = Object.create(null);

  Array.prototype.forEach.call(str1, function (a) {
    count[a] = (count[a] || 0) + 1;
  });

  return Array.prototype.every.call(str2, function (a) {
    return count[a]--;
  });
}

最开始的时候我用了 indexOf 来查找 str1 是否存在 str2 中的字符，跑测试的时候超时了。
果然还是效率太低了。构造对象之后，使用 key:value 的方式寻找效率更好。

Next post: 2019:我这一年

Klay's Notebook

阿胡的的流水账

CamelCase Method

解法

Format a string of names like ‘Bart, Lisa & Maggie’

解法

scramble

我的解法