Determine if String Halves Are Alike

Problem Statement

Imagine you are given a string, s, which always has an even length. Your task involves processing this string to determine if two substrings of s are "alike." Here's how you would go about it:

1. First, divide the string, s, into two equal halves; the first half is labelled as a, and the second half is labelled as b.
2. The two substrings, a and b, are considered alike if both contain the same number of vowels. The vowels in question are a, e, i, o, and u, as well as their uppercase counterparts.
3. Vowels should be counted regardless of their case, meaning both 'A' and 'a' count as the same vowel.
4. Depending on whether a and b have an equal number of vowels, you will then return true if they do, and false if they don't.

This problem requires you primarily to analyze and manipulate strings, also dealing with fundamental operations like substring extraction and character counting.

Examples

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 and Intuition

Let's delve into how one might solve this problem, using the given examples to illustrate:

• Example 1: For the string s = "book", the substrings are a = "bo" and b = "ok". Counting the vowels:

  • a has 1 vowel (o).
  • b also has 1 vowel (o).
  • Since both substrings have the same number of vowels, they are alike. Thus, the function would return true.

• Example 2: For the string s = "textbook", the substrings are a = "text" and b = "book".

  • a contains 1 vowel (e).
  • b contains 2 vowels (o, and o counted twice).
  • The counts differ, so a and b are not alike, meaning the function would return false.

Approach:

• First, define what counts as a vowel using a set or list for quick checking.
• Split the string exactly in the middle.
• Iterate through each half, counting the occurrence of vowels.
• Compare the counts.
• Return true if the counts match (alike), or false if they do not match.

This method relies primarily on linear traversal of the string halves and basic counting operations, making it straightforward yet efficient given the problem constraints.

Solutions

class Solution {
public:
    bool halvesAreAlike(string str) {
        int len = str.length();
        return vowelCount(0, len / 2, str) == vowelCount(len / 2, len, str);
    }
    
    int vowelCount(int start, int end, string& str) {
        string vowelSet = "aeiouAEIOU";
        int count = 0;
        for (int index = start; index < end; index++) {
            if (vowelSet.find(str[index]) != string::npos) {
                count++;
            }
        }
        return count;
    }
};