LeetCode-in-Java
151. Reverse Words in a String
Medium
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 <= 104scontains 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?
Solution
public class Solution {
public String reverseWords(String s) {
StringBuilder sb = new StringBuilder();
int i = s.length() - 1;
while (i >= 0) {
if (s.charAt(i) == ' ') {
i--;
continue;
}
int start = s.lastIndexOf(' ', i);
sb.append(' ');
sb.append(s, start + 1, i + 1);
i = start - 1;
}
if (!sb.isEmpty()) {
sb.deleteCharAt(0);
}
return sb.toString();
}
}