2490. 回环句
2490. 回环句
题目
A sentence is a list of words that are separated by asingle 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"].
- leetcod e 's last character is equal to e xercises's first character.
- exercise s 's last character is equal to s ound's first character.
- soun d 's last character is equal to d elightful's first character.
- delightfu l 's last character is equal to l eetcode's first character.
The sentence is circular.
Example 2:
Input: sentence = "eetcode"
Output: true
Explanation: The words in sentence are ["eetcode"].
- eetcod e 's last character is equal to e etcode'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"].
- Leetcod e 's last character is not equal to i s'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.
题目大意
句子 是由单个空格分隔的一组单词,且不含前导或尾随空格。
- 例如,
"Hello World"
、"HELLO"
、"hello world hello world"
都是符合要求的句子。
单词 仅 由大写和小写英文字母组成。且大写和小写字母会视作不同字符。
如果句子满足下述全部条件,则认为它是一个 回环句 :
- 单词的最后一个字符和下一个单词的第一个字符相等。
- 最后一个单词的最后一个字符和第一个单词的第一个字符相等。
例如,"leetcode exercises sound delightful"
、"eetcode"
、"leetcode eats soul"
都是回环句。然而,"Leetcode is cool"
、"happy Leetcode"
、"Leetcode"
和 "I like Leetcode"
都 不 是回环句。
给你一个字符串 sentence
,请你判断它是不是一个回环句。如果是,返回 true
;否则,返回 false
。
示例 1:
输入: sentence = "leetcode exercises sound delightful"
输出: true
解释: 句子中的单词是 ["leetcode", "exercises", "sound", "delightful"] 。
- leetcod** e** 的最后一个字符和 e xercises 的第一个字符相等。
- exercise s 的最后一个字符和 s ound 的第一个字符相等。
- s ound 的最后一个字符和 delightfu l 的第一个字符相等。
- delightfu l 的最后一个字符和 l eetcode 的第一个字符相等。
这个句子是回环句。
示例 2:
输入: sentence = "eetcode"
输出: true
解释: 句子中的单词是 ["eetcode"] 。
- eetcod e 的最后一个字符和 e etcod e 的第一个字符相等。
这个句子是回环句。
示例 3:
输入: sentence = "Leetcode is cool"
输出: false
解释: 句子中的单词是 ["Leetcode", "is", "cool"] 。
- Leetcod e 的最后一个字符和 i s 的第一个字符 不 相等。
这个句子 不 是回环句。
提示:
1 <= sentence.length <= 500
sentence
仅由大小写英文字母和空格组成sentence
中的单词由单个空格进行分隔- 不含任何前导或尾随空格
解题思路
- 先将输入的字符串
sentence
按空格分割成一个单词数组arr
; - 遍历数组,依次对比当前单词的最后一个字符
lastChar
与下一个单词的第一个字符nextFirstChar
是否一样; - 注意边界情况,最后一个单词的最后一个字符,要和第一个单词的第一个字符相等;
- 一旦发现不相等的情况,立刻返回
false
; - 遍历完还没有发现不相等的情况,则返回
true
。
复杂度分析
- 时间复杂度:
O(n)
,其中n
是句子中的单词数量,需要遍历所有的单词。 - 空间复杂度:
O(n)
,需要额外的数组存储所有单词。
代码
/**
* @param {string} sentence
* @return {boolean}
*/
var isCircularSentence = function (sentence) {
const arr = sentence.split(' '),
n = arr.length;
for (let i = 0; i < n; i++) {
const lastChar = arr[i][arr[i].length - 1];
const nextFirstChar = arr[(i + 1) % n][0];
if (lastChar !== nextFirstChar) return false;
}
return true;
};
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