Palindrome

A palindrome is a word that is spelled the same forwards and backwards. For example, kayak and rotator are both palindromes. hello and world are not palindromes.

Instructions

Create a function called palindrome() that takes a string as an argument and returns true if the string is a palindrome and false if it is not.

Tests

const palindrome = require('./palindrome');

describe('palindrome', () => {
  it('should be a function', () => {
    expect(typeof palindrome).toEqual('function');
  });
  it('should return a boolean', () => {
    expect(typeof palindrome('hello')).toEqual('boolean');
  });
  it('should return true if is a palindrome', () => {
    expect(palindrome('kayak')).toBeTruthy();
    expect(palindrome('rotator')).toBeTruthy();
    expect(palindrome('wow')).toBeTruthy();
  });
  it('should return false if is not a palindrome', () => {
    expect(palindrome('hello')).toBeFalsy();
    expect(palindrome('world')).toBeFalsy();
    expect(palindrome('bye')).toBeFalsy();
  });
  it('should return false if includes spaces', () => {
    expect(palindrome(' wow')).toBeFalsy();
    expect(palindrome('wow ')).toBeFalsy();
  });
});

We are testing to make sure that palindrome is a function and that it returns a boolean. We are also testing to make sure that it returns true if the string is a palindrome and false if it is not. It should also return false if the string includes spaces.

Click For Solutions

Solution 1

function palindrome(str) {
  const reversed = str.split('').reverse().join('');
  return str === reversed;
}

This is very similar to one of the solutions for the reverseString problem. We can use the split method to split the string into an array of characters. We can then use the reverse method to reverse the array. Finally, we can use the join method to join the array back into a string. Then we simply need to check if the str is equal to the reversed string.

Solution 2

function palindrome(str) {
  return str.split('').every((char, i) => {
    return char === str[str.length - i - 1];
  });
}

We can use the every method to check if every character in the string is equal to the character at the same index in the reversed string. We can use the str.length - i - 1 to get the index of the character in the reversed string.