1. Implement a function that can rotate k characters in a left-handed string.
BCDA is obtained by turning one character left of ABCD
ABCD left two characters to get CDAB

Train of thought:

We can first turn the k characters that should be rotated, then turn other characters, and finally turn them together to realize the rotation of characters.

Code:

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<string.h>

void Reverse(char *p,char *q)//Flipping strings
{
    while(p < q)  
    {  
        char a = *p;  
        *p = *q;  
        *q = a;  
        p++;  
        q--;  
    }  
}  
void Leftturn(char *a, int len,int n)//Rotate character function
{
       Reverse(&a[0],&a[n-1]);//Flip first k characters
       Reverse(&a[n],&a[len-1]);//Flip other characters
       Reverse(&a[0],&a[len-1]);//Flip all characters together

}
int main()
{
    char arr[] = "ABCDE";
    int s = 0;
    int sz = strlen(arr);
    printf("Please enter the number of characters you want to rotate\n");
    scanf("%d",&s);
    Leftturn(arr,sz,s);
    printf("%s",arr);
    return 0;
}

2. Judge whether a string is a string after another string rotation.
For example: given s1 = AABCD and s2 = BCDAA, return 1, given s1=abcd and s2=ACBD, return 0

AABCD left one character to get ABCDA
AABCD left two characters to get BCDAA

AABCD right turns a character to get DAABC

Train of thought:

On the basis of the previous question, we make right-handed, and use strcmp function to verify.

Code:

#include<stdio.h>
#include<string.h>
#include<stdlib.h> 
void Reverse(char *p,char *q)
{
    while(p < q)  
    {  
        char a = *p;  
        *p = *q;  
        *q = a;  
        p++;  
        q--;  
    }  
}  
int  Judgeturn(char a[],char b[], int len)
{
        int i = 0;
        char *p = malloc(len);//Open up a dynamic space
        //  Levo
        for(i=0; i<len; i++)
        {
          strcpy(p,a);//Copy a string to dynamic p
          Reverse(&p[0],&p[i]);
          Reverse(&p[i+1],&p[len-1]);
          Reverse(&p[0],&p[len-1]);
          if(strcmp(p,b) == 0)//Comparison and verification of rotated string p and string b
          {
          return 1;
          }

        }
        // Dextral rotation
        for(i=0; i<len; i++)
        {
          strcpy(p,a);
          Reverse(&p[len-i],&p[len-1]);
          Reverse(&p[0],&p[len-i-1]);
          Reverse(&p[0],&p[len-1]);
          if(strcmp(p,b) == 0)
          {
          return 1;
          }
        }  
     return 0;
     free(p);

}
int main()
{
    char arr[] = "ABCDE"; 
    char s[] = "DEABC"; 
    int sz = strlen(arr);
    int ret = 0;
    ret = Judgeturn(arr,s,sz);
    if( ret == 1)
    {
    printf("It is obtained by rotating the original string\n");
    }
    else
    {
        printf("Not derived from the rotation of the original string\n");
    }

    return 0;
}