字符串左旋、右旋

左旋：左旋转操作是把字符串前面的若干个字符转移到字符串的尾部。

1.

#include <iostream>
#include <string>

using namespace std;

string righttrans(int k, string s){
    int n = s.length();
    string res(n, ' ');
    if(k > n) k %= n;

    for(int i = 0; i < k; i++){
        res[n - k + i] = s[i];
    }
    for(int i = 0; i < n - k; i++){
        res[i] = s[k + i];
    }

    return res;
}

int main(){
    int k;
    cin >> k;
    string s;
    cin >> s;
    string res = righttrans(k, s);
    cout << res << endl;
    return 0;
}

右旋：将后面k个元素移至最前

#include <iostream>
#include <string>

using namespace std;

string righttrans(int k, string s){
    int n = s.length();
    string res(n, ' ');
    if(k > n) k %= n;

    for(int i = 0; i < k; i++){
        res[i] = s[n - k + i];
    }
    for(int i = 0; i < n - k; i++){
        res[k + i] = s[i];
    }

    return res;
}

int main(){
    int k;
    cin >> k;
    string s;
    cin >> s;
    string res = righttrans(k, s);
    cout << res << endl;
    return 0;
}

 2.不能申请额外空间，只能在本串上操作：使用整体反转+局部反转

#include <iostream>
#include <string>

using namespace std;

void reverse(string& s, int begin, int end){
    for(begin, end; begin < end; begin++, end--){
        swap(s[begin], s[end]);
    }
}

void righttrans(int k, string& s){
    int n = s.size();
    reverse(s, 0, n-1);
    reverse(s, 0, k-1);
    reverse(s, k, n-1);
}

int main(){
    int k;
    cin >> k;
    string s;
    cin >> s;
    righttrans(k, s);
    cout << s << endl;
    return 0;
}