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.

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

Solution for 1704. Determine if String Halves Are Alike

Approach

1. Define a helper function count_vowels to count the number of vowels in a given string.
2. Compute the length of the input string and find the midpoint.
3. Split the string into two halves: the first half (first_half) and the second half (second_half).
4. Use the count_vowels function to count the vowels in both halves.
5. Compare the counts of vowels in both halves. If they are equal, return True; otherwise, return False.

Code in Different Languages

Python

Written by @YourUsername

class Solution:
    def halvesAreAlike(self, s: str) -> bool:
        def count_vowels(string):
            vowels = set('aeiouAEIOU')
            return sum(1 for char in string if char in vowels)

        length = len(s)
        mid_point = length // 2

        first_half = s[:mid_point]
        second_half = s[mid_point:]

        return count_vowels(first_half) == count_vowels(second_half)

Java

Written by @YourUsername

import java.util.HashSet;
import java.util.Set;

public class Solution {
    public boolean halvesAreAlike(String s) {
        Set<Character> vowels = new HashSet<>();
        vowels.add('a'); vowels.add('e'); vowels.add('i'); vowels.add('o'); vowels.add('u');
        vowels.add('A'); vowels.add('E'); vowels.add('I'); vowels.add('O'); vowels.add('U');

        int length = s.length();
        int midPoint = length / 2;

        String firstHalf = s.substring(0, midPoint);
        String secondHalf = s.substring(midPoint);

        return countVowels(firstHalf, vowels) == countVowels(secondHalf, vowels);
    }

    private int countVowels(String str, Set<Character> vowels) {
        int count = 0;
        for (char c : str.toCharArray()) {
            if (vowels.contains(c)) {
                count++;
            }
        }
        return count;
    }
}

C++

Written by @YourUsername

#include <bits/stdc++.h>
using namespace std;

class Solution {
public:
    bool halvesAreAlike(string s) {
        auto countVowels = [](const string& str) {
            unordered_set<char> vowels{'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'};
            int count = 0;
            for (char c : str) {
                if (vowels.count(c) > 0) {
                    count++;
                }
            }
            return count;
        };

        int length = s.length();
        int midPoint = length / 2;

        string firstHalf = s.substr(0, midPoint);
        string secondHalf = s.substr(midPoint);

        return countVowels(firstHalf) == countVowels(secondHalf);
    }
};

Complexity Analysis

• Time Complexity: $O(N)$
• Space Complexity: $O(1)$

References

• LeetCode Problem: Determine if String Halves Are Alike
• Solution Link: LeetCode Solution