Hj13 sentence reverse order

​​​​​​HJ13 The sentence is in reverse order

#include<iostream>
#include<cstring>
#include<vector>
using namespace std;

class Solution {
private:
    static bool charInStr(char c, const char *sep) {
        bool b = false;
        for (int i = 0; sep[i] != '\0'; i++) {
            if (c == sep[i]) {
                b = true;
                break;
            }
        }
        return b;
    }
    std::vector<std::string> explode(const char *sep, std::string s) {
        std::vector<std::string> vs;
        int i = 0;
        for (; i <s.size(); i++) {
            if (false == charInStr(s[i], sep)) {
                break;
            }
        }
        int j = i;
        for (; i < s.size(); i++) {
            if (charInStr(s[i], sep)) {
                vs.push_back(s.substr(j, i-j));
                j = i+1;
            }
        }
        if (j < i) {
            vs.push_back(s.substr(j, i-j));
        }
        return vs;
    }
    static void reverse(std::vector<std::string> &vs) {
        std::string word;
        for (int i = 0, j = vs.size()-1; i < j; i++, j--) {
            word = vs[i];
            vs[i] = vs[j];
            vs[j] = word;
        }
    }

    static char *join(const std::vector<std::string>& words, std::string delim) {
        size_t sz = 0;
        std::vector<std::string>::const_iterator it;
        for (it = words.begin(); it != words.end(); ++it) {
            sz += it->size();
        }
        sz += delim.size() * (words.size()-1);
        sz += 1;

        char *ans = (char *)malloc(sizeof(char) * sz);
        char *p = ans;
        it = words.begin();
        ::strncpy(ans, it->c_str(), it->size());
        p += it->size();
        ++it;
        for (; it != words.end(); ++it) {
            ::strncpy(p, delim.c_str(), delim.size());
            p += delim.size();
            ::strncpy(p, it->c_str(), it->size());
            p += it->size();
        }

        return ans;
    }
public:
    char *reverseWords(std::string line) {
        std::vector<std::string> words = explode(" \t\r\n", std::move(line));
        reverse(words);
//        for (auto w : words) {
//            std::cout << w << std::endl;
//        }
        return join(words, " ");
    }
};

int main(){
     char line[1000] = {'\0'};
     std::cin.getline(line, 1000);
//     strcpy(line, "I am a boy");

    Solution s;
    char *ans = s.reverseWords(std::string(line));
    std::cout << ans << std::endl;
    free(ans);
    return 0;
}