1704. Determine if String Halves Are Alike

Problem

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.

Solution

/**
 * @param {string} s
 * @return {boolean}
 */
var halvesAreAlike = function(s) {
    var map = {
        a: true,
        e: true,
        i: true,
        o: true,
        u: true,
        A: true,
        E: true,
        I: true,
        O: true,
        U: true,
    };
    var half = s.length / 2;
    var count = 0;
    for (var i = 0; i < half; i++) {
        if (map[s[i]]) count++;
        if (map[s[i + half]]) count--;
    }
    return count === 0;
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(1).