Question

2586. Count the Number of Vowel Strings in Range

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Description

You are given a 0-indexed array of string words and two integers left and right.

A string is called a vowel string if it starts with a vowel character and ends with a vowel character where vowel characters are 'a', 'e', 'i', 'o', and 'u'.

Return _the number of vowel strings _words[i]_ where _i_ belongs to the inclusive range _[left, right].

 

Example 1:

Input: words = ["are","amy","u"], left = 0, right = 2
Output: 2
Explanation: 
- "are" is a vowel string because it starts with 'a' and ends with 'e'.
- "amy" is not a vowel string because it does not end with a vowel.
- "u" is a vowel string because it starts with 'u' and ends with 'u'.
The number of vowel strings in the mentioned range is 2.

Example 2:

Input: words = ["hey","aeo","mu","ooo","artro"], left = 1, right = 4
Output: 3
Explanation: 
- "aeo" is a vowel string because it starts with 'a' and ends with 'o'.
- "mu" is not a vowel string because it does not start with a vowel.
- "ooo" is a vowel string because it starts with 'o' and ends with 'o'.
- "artro" is a vowel string because it starts with 'a' and ends with 'o'.
The number of vowel strings in the mentioned range is 3.

 

Constraints:

• 1 <= words.length <= 1000
• 1 <= words[i].length <= 10
• words[i] consists of only lowercase English letters.
• 0 <= left <= right < words.length

Solutions

Solution 1: Simulation

We just need to traverse the string in the interval $[left,.. right]$, and check if it starts and ends with a vowel. If so, the answer plus one.

After the traversal, return the answer.

The time complexity is $O(m)$, and the space complexity is $O(1)$. Where $m = right - left + 1$.

class Solution:
  def vowelStrings(self, words: List[str], left: int, right: int) -> int:
    return sum(
      w[0] in 'aeiou' and w[-1] in 'aeiou' for w in words[left : right + 1]
    )

class Solution {
  public int vowelStrings(String[] words, int left, int right) {
    int ans = 0;
    for (int i = left; i <= right; ++i) {
      var w = words[i];
      if (check(w.charAt(0)) && check(w.charAt(w.length() - 1))) {
        ++ans;
      }
    }
    return ans;
  }

  private boolean check(char c) {
    return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u';
  }
}

class Solution {
public:
  int vowelStrings(vector<string>& words, int left, int right) {
    auto check = [](char c) -> bool {
      return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u';
    };
    int ans = 0;
    for (int i = left; i <= right; ++i) {
      auto w = words[i];
      ans += check(w[0]) && check(w[w.size() - 1]);
    }
    return ans;
  }
};

func vowelStrings(words []string, left int, right int) (ans int) {
  check := func(c byte) bool {
    return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u'
  }
  for _, w := range words[left : right+1] {
    if check(w[0]) && check(w[len(w)-1]) {
      ans++
    }
  }
  return
}

function vowelStrings(words: string[], left: number, right: number): number {
  let ans = 0;
  const check: string[] = ['a', 'e', 'i', 'o', 'u'];
  for (let i = left; i <= right; ++i) {
    const w = words[i];
    if (check.includes(w[0]) && check.includes(w.at(-1))) {
      ++ans;
    }
  }
  return ans;
}

impl Solution {
  pub fn vowel_strings(words: Vec<String>, left: i32, right: i32) -> i32 {
    let check = |c: u8| -> bool {
      c == b'a' || c == b'e' || c == b'i' || c == b'o' || c == b'u'
    };

    let mut ans = 0;
    for i in left..=right {
      let w = words[i as usize].as_bytes();
      if check(w[0]) && check(w[w.len() - 1]) {
        ans += 1;
      }
    }

    ans
  }
}