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.

Example 3:

Input: s = "MerryChristmas"
Output: false

Example 4:

Input: s = "AbCdEfGh"
Output: true

Constraints:

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

Solution

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

class Solution {
public:
    bool halvesAreAlike(string s) {
        const int s_len = s.length();
        const string vowels = "aeiouAEIOU";
        int cnt1 = 0, cnt2 = 0;
        for (int i=0; i<s_len; ++i) {
            if (vowels.find(s[i]) != string::npos) {
                if (i<s_len/2) ++cnt1;
                else ++cnt2;
            }
        }
        return cnt1 == cnt2;
    }
};