151. 反转字符串中的单词
151. 反转字符串中的单词
题目
Given an input string s
, reverse the order of the words.
A word is defined as a sequence of non-space characters. The words in s
will be separated by at least one space.
Return a string of the words in reverse order concatenated by a single space.
Note that s
may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.
Example 1:
Input: s = "the sky is blue"
Output: "blue is sky the"
Example 2:
Input: s = " hello world "
Output: "world hello"
Explanation: Your reversed string should not contain leading or trailing spaces.
Example 3:
Input: s = "a good example"
Output: "example good a"
Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.
Constraints:
1 <= s.length <= 10^4
s
contains English letters (upper-case and lower-case), digits, and spaces' '
.- There is at least one word in
s
.
Follow-up: If the string data type is mutable in your language, can you solve it in-place with O(1)
extra space?
题目大意
给定一个字符串,逐个翻转字符串中的每个单词。
说明:
- 无空格字符构成一个单词。
- 输入字符串可以在前面或者后面包含多余的空格,但是反转后的字符不能包括。
- 如果两个单词间有多余的空格,将反转后单词间的空格减少到只含一个。
请尝试使用 O(1)
额外空间复杂度的 原地 解法。
解题思路
思路一:分割+倒序
常规的方式是把 s
按空格 split
成若干单词,然后 reverse
这些单词的顺序,最后把这些单词 join
成句子。
复杂度分析
- 时间复杂度:
O(n)
,其中n
为字符串s
的长度;split()
方法为O(n)
reverse()
方法为O(n)
filter()
方法为O(n)
join()
方法为O(n)
- 空间复杂度:
O(n)
,新建的字符串数组总长度≤n
,占用O(n)
大小的额外空间。
思路二:双指针
- 倒序遍历字符串
s
,记录单词左右索引边界i
,j
。 - 每确定一个单词的边界,则将其添加至单词列表
res
。 - 最终,将单词列表拼接为字符串,并返回即可。
复杂度分析
- 时间复杂度:
O(n)
,其中n
为字符串s
的长度; - 空间复杂度:
O(1)
代码
/**
* @param {string} s
* @return {string}
*/
var reverseWords = function (s) {
return s
.split(' ')
.reverse()
.filter((i) => i != '')
.join(' ');
};
/**
* @param {string} s
* @return {string}
*/
var reverseWords = function (s) {
s = s.trim();
let i = (j = s.length - 1),
res = '';
while (i >= 0) {
while (i >= 0 && s[i] != ' ') {
i--;
}
res += s.slice(i + 1, j + 1);
while (i >= 0 && s[i] == ' ') {
i--;
}
j = i;
if (i != -1) {
res += ' ';
}
}
return res;
};
相关题目
题号 | 标题 | 题解 | 标签 | 难度 |
---|---|---|---|---|
186 | 反转字符串中的单词 II 🔒 | 双指针 字符串 |