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}

1#include <iostream>
2#include <algorithm>

void reverseWord(char* s, int start, int end) {
    while (start < end) {
        std::swap(s[start++], s[end--]);
    }
}

std::string reverseWords(std::string s) {
    // Reverse the whole string
    std::reverse(s.begin(), s.end());

    int n = s.length(), wordStart = 0, resultIndex = 0;

    while (wordStart < n) {
        while (wordStart < n && s[wordStart] == ' ') wordStart++;
        if (wordStart == n) break;

        int wordEnd = wordStart;
        while (wordEnd < n && s[wordEnd] != ' ') wordEnd++;

        std::reverse(s.begin() + wordStart, s.begin() + wordEnd);
        if (resultIndex > 0) s[resultIndex++] = ' ';

        while (wordStart < wordEnd) s[resultIndex++] = s[wordStart++];
    }
    s.resize(resultIndex);
    return s;
}

int main() {
    std::string input = "  hello world  ";
    std::cout << reverseWords(input) << std::endl;
    return 0;
}