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Java-based LeetCode algorithm problem solutions, regularly updated

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package g2401_2500.s2490_circular_sentence;

// #Easy #String #2023_01_27_Time_1_ms_(99.85%)_Space_42.6_MB_(55.63%)

/**
 * 2490 - Circular Sentence\.
 *
 * Easy
 *
 * 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.
**/
public class Solution {
    public boolean isCircularSentence(String sentence) {
        char[] letters = sentence.toCharArray();
        int len = letters.length;
        for (int i = 0; i < len - 1; ++i) {
            if (letters[i] == ' ' && letters[i - 1] != letters[i + 1]) {
                return false;
            }
        }
        return letters[0] == letters[len - 1];
    }
}