1#include <stdio.h>
2#include <string.h>
3#include <stdlib.h>
4
5char* reverseWords(char *s) {
6    // calculate length
7    int len = strlen(s), start = 0, wordCount = 0;
8    char *temp = malloc(len + 1);
9    char *result = malloc(len + 1);
10    temp[0] = '\0'; result[0] = '\0';
11    
12    // trim leading and trailing spaces
13    while (s[start] == ' ') start++;
14    int end = len - 1;
15    while (s[end] == ' ') end--;
16    
17    for (int i = start; i <= end; i++) {
18        if (s[i] != ' ') {
19            strncat(temp, &s[i], 1);
20        } else if (s[i] == ' ' && (i == start || s[i - 1] != ' ')) {
21            strcat(temp, " ");
22        }
23    }
24    char *token = strtok(temp, " ");
25    while (token != NULL) {
26        if (wordCount > 0) {
27            memmove(result + strlen(token) + 1, result, strlen(result) + 1);
28            memcpy(result, " ", 1);
29        }
30        memmove(result + strlen(token), result, strlen(result) + 1);
31        memcpy(result, token, strlen(token));
32        token = strtok(NULL, " ");
33        wordCount++;
34    }
35    free(temp);
36    return result;
37}
38
39int main() {
40    char input[] = "  hello world  ";
41    char* output = reverseWords(input);
42    printf("%s\n", output);
43    free(output);
44    return 0;
45}

1using System;
using System.Text;

public class Solution {
    public static string ReverseWords(string s) {
        char[] chars = s.Trim().ToCharArray();
        int n = chars.Length;

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

        Reverse(0, n - 1);

        int rightIndex = 0;
        for (int i = 0; i < n; ++i) {
            if (chars[i] == ' ') continue;
            int start = i;
            while (i < n && chars[i] != ' ') i++;
            Reverse(start, i - 1);
            while (start < i) chars[rightIndex++] = chars[start++];
            if (rightIndex < n) chars[rightIndex++] = ' ';
        }

        return new String(chars, 0, rightIndex == 0 ? 0 : rightIndex - 1);
    }

    public static void Main() {
        string input = "  hello world  ";
        string output = ReverseWords(input);
        Console.WriteLine(output);
    }
}