알고리즘 기초-1

reverse string

// --- Directions
// Given a string, return a new string with the reversed
// order of characters
// --- Examples
//   reverse('apple') === 'leppa'
//   reverse('hello') === 'olleh'
//   reverse('Greetings!') === '!sgniteerG'

function reverse1(str) {
  const arr = str.split('');
  arr.reverse();
  return arr.join();
  // Save as => str.split('').reverse().join();
}

function reverse2(str) {
  let reversed = '';
  for (const character of str) {
    reversed = character + reversed;
  }
  return reversed;
}

function reverse3(str) {
  str.split('').reduce((reversed, character) => {
    return character + reversed;
  }, '');
  return reversed;
}

palindrome

// --- Directions
// Given a string, return true if the string is a palindrome
// or false if it is not.  Palindromes are strings that
// form the same word if it is reversed. *Do* include spaces
// and punctuation in determining if the string is a palindrome.
// --- Examples:
//   palindrome("abba") === true
//   palindrome("abcdefg") === false

// 위 reverse string 문제를 활용한 방법.
function palindrome1(str) {
    const reversed = str.split('').reverse().join('');
    return str === reversed;
}

// every 메소드를 활용해 한글자씩 비교하여 해결하는 방법.
function palindrome2(str) {
    return str.split('').every((char, i) => {
        return char === str[str.length - i - 1];
    })
}

reverse int

// --- Directions
// Given an integer, return an integer that is the reverse
// ordering of numbers.
// --- Examples
//   reverseInt(15) === 51
//   reverseInt(981) === 189
//   reverseInt(500) === 5
//   reverseInt(-15) === -51
//   reverseInt(-90) === -9

function reverseInt1(n) {
    const reversed = n.toString().split('').reverse().join('');
    return parseInt(reversed) * Math.sign(n);
}

module.exports = reverseInt;