这题我直接想到的是istringstream 和 stack 但不知道这样使用是不是违反了规定

class Solution {
public:string reverseWords(string s) {istringstream iss(s);string word;stack<string> st;string res;while (iss >> word) {st.push(word);}while (!st.empty()) {res += st.top();st.pop();if (!st.empty()) {res += " ";}}return res;}
};

看了卡哥的O(1)空间复杂度解法，写了下述代码

class Solution {
public:void removeSpaces(string &s) {int left = 0;int right = 0;int len = s.size();while (right < len) {if (s[right] != ' ') {if (left != 0) {s[left++] = ' ';}while (right < len && s[right] != ' ') {s[left++] = s[right++];}} else {right++;}}s.resize(left);}string reverseWords(string s) {removeSpaces(s);reverse(s.begin(), s.end());int left = 0;int right = 0;int len = s.size();while (right < len) {while (right < len && s[right] != ' ') {right++;}reverse(s.begin() + left, s.begin() + right);left = ++right;}return s;}
};

方法很巧妙

#include<iostream>
#include<algorithm>
using namespace std;
int main() {int n;string s;cin >> n;cin >> s;int len = s.size(); //获取长度reverse(s.begin(), s.begin() + len - n);reverse(s.begin() + len - n, s.end());reverse(s.begin(), s.end());cout << s << endl;
}