Beginners sincerely ask for advice about string - string

Question

What the class describes is about "reversing a string", which is correct and usable from the Leetcode website. Today, I want to present "reversing a string" by inputting a value by myself (such as the int main() part below), but I still can't execute it after thinking for a long time. Beginners sincerely ask for advice, maybe you can also attach your writing so that I can learn, thank you.
#include <iostream>
#include <string>
using namespace std;
class Solution
{
public:
string reverseWords(string s)
{
if (s.size() == 0)
{
return s;
}
int front = 0, back = 0;
for (int i = 0; i < s.size() - 1; i++)
{
if (s[i] != ' ')
{
back++;
}
else
{
reverse(s.begin() + front, s.begin() + back);
front = back + 1;
back = front;
}
}
back++;
reverse(s.begin() + front, s.begin() + back);
return s;
}
};
int main()
{
Solution word01;
string s1= "Hello caterpillar";
word01 s1;
cout << s1.reverseWords();
}

Answer 1

Your code is pretty good, however we just want to reverse the words not the chars, for that we can use a while loop.
Similarly using two pointers, this'd pass just fine:
// The following block might trivially improve the exec time;
// Can be removed;
static const auto __optimize__ = []() {
std::ios::sync_with_stdio(false);
std::cin.tie(NULL);
std::cout.tie(NULL);
return 0;
}();
// Most of headers are already included;
// Can be removed;
#include <cstdint>
#include <string>
#include <algorithm>
static const struct Solution {
using ValueType = std::uint_fast16_t;
std::string reverseWords(std::string s) {
std::reverse(std::begin(s), std::end(s));
ValueType len = std::size(s);
ValueType index = 0;
for (auto left = 0; left < len; ++left) {
if (s[left] != ' ') {
if (index) {
s[index++] = ' ';
}
ValueType right = left;
while (right < len && s[right] != ' ') {
s[index++] = s[right++];
}
std::reverse(std::begin(s) + index - (right - left), std::begin(s) + index);
left = right;
}
}
s.erase(std::begin(s) + index, std::end(s));
return s;
}
};
Here is LeetCode's solution with comments:
class Solution {
public:
string reverseWords(string s) {
// reverse the whole string
reverse(s.begin(), s.end());
int n = s.size();
int idx = 0;
for (int start = 0; start < n; ++start) {
if (s[start] != ' ') {
// go to the beginning of the word
if (idx != 0) s[idx++] = ' ';
// go to the end of the word
int end = start;
while (end < n && s[end] != ' ') s[idx++] = s[end++];
// reverse the word
reverse(s.begin() + idx - (end - start), s.begin() + idx);
// move to the next word
start = end;
}
}
s.erase(s.begin() + idx, s.end());
return s;
}
};
References
For additional details, please see the Discussion Board where you can find plenty of well-explained accepted solutions with a variety of languages including low-complexity algorithms and asymptotic runtime/memory analysis1, 2.