2490. Circular Sentence
Difficulty: Easy
Topics: String
A sentence is a list of words that are separated by a single space with no leading or trailing spaces.
- For example,
"Hello World"
,"HELLO"
,"hello world hello world"
are all sentences.
Words consist of only uppercase and lowercase English letters. Uppercase and lowercase English letters are considered different.
A sentence is circular if:
- The last character of a word is equal to the first character of the next word.
- The last character of the last word is equal to the first character of the first word.
For example, "leetcode exercises sound delightful"
, "eetcode"
, "leetcode eats soul"
are all circular sentences. However, "Leetcode is cool"
, "happy Leetcode"
, "Leetcode"
and "I like Leetcode"
are not circular sentences.
Given a string sentence
, return _true
if it is circular_. Otherwise, return false
.
Example 1:
- Input: sentence = "leetcode exercises sound delightful"
- Output: true
-
Explanation: The words in sentence are ["leetcode", "exercises", "sound", "delightful"].
- leetcode's last character is equal to exercises's first character.
- exercises's last character is equal to sound's first character.
- sound's last character is equal to delightful's first character.
- delightful's last character is equal to leetcode's first character.
- The sentence is circular.
Example 2:
- Input: sentence = "eetcode"
- Output: true
-
Explanation: The words in sentence are ["eetcode"].
- eetcode's last character is equal to eetcode's first character.
- The sentence is circular.
Example 3:
- Input: sentence = "Leetcode is cool"
- Output: false
-
Explanation: The words in sentence are ["Leetcode", "is", "cool"].
- Leetcode's last character is not equal to is's first character.
- The sentence is not circular.
Constraints:
1 <= sentence.length <= 500
-
sentence
consist of only lowercase and uppercase English letters and spaces. - The words in
sentence
are separated by a single space. - There are no leading or trailing spaces.
Hint:
- Check the character before the empty space and the character after the empty space.
- Check the first character and the last character of the sentence.
Solution:
We need to verify two conditions:
- Each word’s last character should match the next word’s first character.
- The last character of the final word should match the first character of the first word, making it circular.
Let's implement this solution in PHP: 2490. Circular Sentence
<?php
/**
* @param String $sentence
* @return Boolean
*/
function isCircularSentence($sentence) {
...
...
...
/**
* go to ./solution.php
*/
}
// Test cases
$sentence1 = "leetcode exercises sound delightful";
$sentence2 = "eetcode";
$sentence3 = "Leetcode is cool";
echo isCircularSentence($sentence1) ? "true\n" : "false\n"; // Output: true
echo isCircularSentence($sentence2) ? "true\n" : "false\n"; // Output: true
echo isCircularSentence($sentence3) ? "true\n" : "false\n"; // Output: false
?>
Explanation:
-
Splitting the Sentence: Use
explode(" ", $sentence)
to split the sentence into words. -
Looping through Words:
- For each word, get its last character using
substr($words[$i], -1)
. - Get the first character of the next word. For the last word, we use modulo (
%
) to wrap around to the first word.
- For each word, get its last character using
-
Comparison:
- If the last character of a word doesn’t match the first character of the next word, return
false
. - If the loop completes without finding any mismatch, the sentence is circular, so return
true
.
- If the last character of a word doesn’t match the first character of the next word, return
This code efficiently checks the circular condition for each word pair, making it simple and optimal.
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