1using System;
2
3public class Solution {
4    public static void ReverseWords(string s) {
5        char[] arr = s.ToCharArray();
6        int start = 0;
7
8        for (int end = 0; end < arr.Length; end++) {
9            if (arr[end] == ' ' || end == arr.Length - 1) {
10                Reverse(arr, start, (end == arr.Length - 1) ? end : end - 1);
11                start = end + 1;
12            }
13        }
14        Console.WriteLine(new String(arr));
15    }
16
17    private static void Reverse(char[] arr, int start, int end) {
18        while (start < end) {
19            char temp = arr[start];
20            arr[start] = arr[end];
21            arr[end] = temp;
22            start++;
23            end--;
24        }
25    }
26
27    public static void Main() {
28        string s = "Let's take LeetCode contest";
29        ReverseWords(s);
30    }
31}

1using System;
2
public class Solution {
    public static void ReverseWords(string s) {
        char[] arr = s.ToCharArray();
        int start = 0;

        for (int end = 0; end <= arr.Length; end++) {
            if (end == arr.Length || arr[end] == ' ') {
                Reverse(arr, start, end - 1);
                start = end + 1;
            }
        }
        Console.WriteLine(new String(arr));
    }

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

    public static void Main() {
        string s = "Let's take LeetCode contest";
        ReverseWords(s);
    }
}