solutions: 1704 - Determine if String Halves Are Alike (Easy)

solutions/1700-1799/1704-determine-if-string-halves-are-alike-easy.md

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+---
+description: 'Author: @heder, @wingkwong | https://leetcode.com/problems/determine-if-string-halves-are-alike/'
+tags: [String, Counting]
+---
+
+# 1704 - Determine if String Halves Are Alike (Easy) 
+
+## Problem Link
+
+https://leetcode.com/problems/determine-if-string-halves-are-alike/
+
+## Problem Statement
+
+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 1: Counting
+
+Well, just count the vowels in each half and compare. Using string_view avoids make a copy of the input.
+
+Clang seems to produce fairly efficient code for isVowel: https://godbolt.org/z/MWra5vb6G -- much shorter than I though it would be and branch-free. @jit posted a nice analysis about the generated code [here](https://leetcode.com/problems/determine-if-string-halves-are-alike/solutions/2865500/c-counting-vowels-and-looking-at-some-assembly/comments/1702118).
+
+- Time complexity is $$O(n)$$ and the
+- Space complexity is $$O(1)$$.
+
+<Tabs>
+<TabItem value="cpp" label="C++">
+<SolutionAuthor name="@heder"/>
+
+```cpp
+static bool halvesAreAlike(const string_view s) noexcept {
+    return vowelCount(s.substr(0, size(s) / 2)) == vowelCount(s.substr(size(s) / 2));
+}
+
+static int vowelCount(const string_view s) noexcept {
+    return count_if(begin(s), end(s), isVowel);
+}
+
+static bool isVowel(char ch) noexcept {
+    return
+        ch == 'a' || ch == 'e' || ch == 'i'  || ch == 'o' || ch == 'u' ||
+        ch == 'A' || ch == 'E' || ch == 'I'  || ch == 'O' || ch == 'U' ;
+}
+```
+
+</TabItem>
+
+
+<TabItem value="rs" label="Rust">
+<SolutionAuthor name="@wingkwong"/>
+
+```rs
+impl Solution {
+    pub fn halves_are_alike(s: String) -> bool {
+        // count the number of vowels in the given string
+        let go = |s: &str| s.chars().filter(|&c| "aeiouAEIOU".contains(c)).count();
+        // check if the count of the first half is same as that of the second half
+        go(&s[..s.len() / 2]) == go(&s[s.len() / 2..])
+    }
+}
+```
+
+</TabItem>
+</Tabs>