Leetcode 557. Reverse Words in a String III

Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example 1:

Input: "Let's take LeetCode contest"
Output: "s'teL ekat edoCteeL tsetnoc"

Note: In the string, each word is separated by single space and there will not be any extra space in the string.

Code (Java):

class Solution {
    public String reverseWords(String s) {
        if (s == null || s.length() < 2) {
            return s;
        }

        int start = 0;
        int end = 0;

        char[] arr = s.toCharArray();

        while (end < s.length()) {
            while (end < s.length() && s.charAt(end) != ' ') {
                end++;
            }
            reverse(arr, start, end - 1);
            end++;
            start = end;
        }

        reverse(arr, start, end - 1);

        return new String(arr);
    }

    private void reverse(char[] arr, int start, int end) {
        while (start < end) {
            char temp = arr[start];
            arr[start] = arr[end];
            arr[end] = temp;
            start++;
            end--;
        }
    }
}