LeetCode 151. Reverse Words in a String

151. Reverse Words in a String

Difficulty: Medium

Given an input string, reverse the string word by word.

Example 1:

Input: "the sky is blue"
Output: "blue is sky the"

Example 2:

Input: "  hello world!  "
Output: "world! hello"
Explanation: Your reversed string should not contain leading or trailing spaces.

Example 3:

Input: "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.

Note:

• A word is defined as a sequence of non-space characters.
• Input string may contain leading or trailing spaces. However, your reversed string should not contain leading or trailing spaces.
• You need to reduce multiple spaces between two words to a single space in the reversed string.

Follow up:

For C programmers, try to solve it in-place in O(1) extra space.

Solution

Language: Java

class Solution {
    public String reverseWords(String s) {
        if (s == null || s.length() == 0) {
            return s;
        }
        LinkedList<String> list = new LinkedList<>();
        int i = 0;
        int start = 0;
        while (i < s.length()) {
            while (i < s.length() && s.charAt(i) == ' ') {
                i++;
            }
            start = i;
            while (i < s.length() && s.charAt(i) != ' ') {
                i++;
            }
            if (start < s.length()) {
                list.addFirst(s.substring(start, i));
            }
        }
        return String.join(" ", list);
    }
}