1704. Determine if String Halves Are Alike

Determine if String Halves Are Alike

Problem Description

You are given a string s of even length. Split this string into two halves of equal lengths, and let a be the first half and b be the second half.

Two strings are alike if they have the same number of vowels ('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'). Notice that s contains uppercase and lowercase letters.

Return true if a and b are alike. Otherwise, return false.

 

Example 1:

Input: s = "book"
Output: true

Explanation: a = "bo" and b = "ok". a has 1 vowel and b has 1 vowel. Therefore, they are alike.

Example 2:

Input: s = "textbook"
Output: false

Explanation: a = "text" and b = "book". a has 1 vowel whereas b has 2. Therefore, they are not alike.
Notice that the vowel o is counted twice.

 

Constraints:

• 2 <= s.length <= 1000
• s.length is even.
• s consists of uppercase and lowercase letters.

Approach) Using Set

/**
 * @param {string} s
 * @return {boolean}
 */
const halvesAreAlike = (
  s,
  vowels = new Set(['A', 'E', 'I', 'O', 'U', 'a', 'e', 'i', 'o', 'u']),
) =>
  ![...s].reduce(
    (acc, curr, idx) =>
      acc + +(vowels.has(curr) ? (idx < s.length / 2 ? 1 : -1) : 0),
    0,
  );

And here is the boring multi-line version everybody craves.

/**
 * @param {string} s
 * @return {boolean}
 */
const halvesAreAlike = s => {
  let sum = 0;
  const vowels = new Set(['A', 'E', 'I', 'O', 'U', 'a', 'e', 'i', 'o', 'u']);
  for (let i = 0; i < s.length / 2; i++)
    sum += vowels.has(s[i]) - vowels.has(s[s.length - 1 - i]);
  return !sum;
};

Approach) One Liner 

It is not readable it is terse

var halvesAreAlike =s=> s.split("").slice(0, s.length/2).reduce((v,e)=>"AEIOU".includes(e.toUpperCase())?v+=1:v, 0) === s.split("").slice(s.length/2).reduce((v,e)=>"AEIOU".includes(e.toUpperCase())?v+=1:v, 0) 

Approach) With Fixed Length Array

const halvesAreAlike = s => {
  const code = new Uint8Array(123);
  const target = 'aeiouAEIOU';
  let a = 0, b = 0;
  for (let i = 0; i < target.length; ++i) {
    code[target.charCodeAt(i)] = 1;
  }
  for (let left = 0, right = s.length - 1; left < right; ++left, --right) {
    a += code[s.charCodeAt(left)];
    b += code[s.charCodeAt(right)];
  }
  return a === b;
};

Approach) Set + Mid

var halvesAreAlike = function(s) {
    let ar = new Set(['a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'])
    
    let mid = s.length / 2
    let countL=0
    for (let word of s) {
        if (ar.has(word)) {
           countL++ 
        }
        mid--
        if (mid === 0){
            countL *= -1
        }
        
    }
    
    return countL === 0;
};

Conclusion

That’s all folks! In this post, we solved LeetCode problem 1704. Determine if String Halves Are Alike

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