LeetCode Js-125. Valid Palindrome

    AllenLi
    LeetCode Js-String

    A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.
    Given a string s, return true if it is a palindrome, or false otherwise.

    如果一個短語是回文，將所有大寫字母轉為小寫字母、刪除所有非字母字符後，該回文向前或向後讀取皆相同。
字母字符包含文字和數值。
給予一個字串 s，如果是回文就回傳 true，否則回傳 false。

ex. Palindrome = level、refer

    Example 1:

    Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.

    Example 2:

    Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.

    Example 3:

    Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.

    Solution:
    1. Input s 轉換成小寫字母。
    2. Input s 將特殊符號移除。
    3. 宣告 reverseWord 為反轉後的 s。
    4. 回傳 s 中符合 reverseWord，完全符合為 0，沒有符合為 -1。

    Code:

    var isPalindrome = function(s) {
  s = s.toLowerCase()
  s = s.replace(/[^a-z0-9]/ig,"")
  let reverseWord = s.split("").reverse().join("")
  
  return s.indexOf(reverseWord) === 0
};

    FlowChart:
    Example 1

    Input: s = "A man, a plan, a canal: Panama"
s.toLowerCase() = a man, a plan, a canal: panama
s.replace = amanaplanacanalpanama
reverseWord = s.split("").reverse().join("") => amanaplanacanalpanama

return true

    Example 2

    Input: s = "race a car"
s.toLowerCase() = race a car
s.replace = raceacar
reverseWord = s.split("").reverse().join("") => racaecar

return false

    Example 3

    Input: s = " "
s.toLowerCase() = ''
s.replace = ''
reverseWord = s.split("").reverse().join("") => ''

return true

    .toLowerCase()

    .toLowerCase()：函式會回傳字符串轉換成英文小寫字母。
const sentence = 'The quick brown fox jumps over the lazy dog.'

console.log(sentence.toLowerCase());
// expected output: "the quick brown fox jumps over the lazy dog."

    .replace()

    .replace(a, b)：符合(a)內的字串後進行替換成(b)，並回傳一個新的字串。
let text = "Mr Blue has a blue house and a blue car";
let result = text.replace(/blue/gi, "red");

console.log(result)
// expected output: "Mr red has a red house and a red car"

    .reverse()

    .reverse()：反轉一個陣列，陣列中的第一個元素變成最後一個，而最後一個元素變成第一個。
const array1 = ['one', 'two', 'three'];
const reversed = array1.reverse();

console.log('reversed:', reversed);
// expected output: "reversed:" Array ["three", "two", "one"]

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