No. 19 - Left Rotation of String

leftRotationOfString.c

//http://codercareer.blogspot.kr/2011/11/no-19-left-rotation-of-string.html
// time complexity : O(n)
// space complexity : O(n)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void Reverse(char *pBegin, char *pEnd) {
  if(pBegin == NULL || pEnd == NULL)
    return;

  while(pBegin < pEnd) {
    char temp = *pBegin;
    *pBegin = *pEnd;
    *pEnd = temp;

    pBegin ++, pEnd --;
  }
}

char* leftRotationOfString(char *pStr, int n) {
/*
  if (string == NULL)
    return NULL;

  int length = strlen(string);
  char tempString[100];
  char *rotationString = string;

  //make string + string
  strcpy(tempString, string);
  strcat(tempString, string);

  for (int i = index; i < length + index; i ++) {
    *rotationString = tempString[i];
    rotationString ++;
  }

  printf("rotation = %s \n", string);

  return string;
*/
  if(pStr != NULL) {
    int nLength = strlen(pStr);
    if(nLength > 0 && n > 0 && n < nLength) {
      char* pFirstStart = pStr;
      char* pFirstEnd = pStr + n - 1;
      char* pSecondStart = pStr + n;
      char* pSecondEnd = pStr + nLength - 1;

      // Reverse the n leading characters
      Reverse(pFirstStart, pFirstEnd);
      // Reverse other characters
      Reverse(pSecondStart, pSecondEnd);
      // Reverse the whole string
      Reverse(pFirstStart, pSecondEnd);
    }
  }

  return pStr;
}

int main(void) {
  printf("test start \n");

  char *inputString = (char *)malloc(sizeof(char) * 50);
  strcpy(inputString, "abcdef");

  printf("input = %s, rotation = %s \n", inputString, leftRotationOfString(inputString, 1));
  printf("input = %s, rotation = %s \n", inputString, leftRotationOfString(inputString, 2));
  printf("input = %s, rotation = %s \n", inputString, leftRotationOfString(inputString, 3));
  printf("input = %s, rotation = %s \n", inputString, leftRotationOfString(inputString, 4));
  printf("input = %s, rotation = %s \n", inputString, leftRotationOfString(inputString, 5));

  free(inputString);
  return 0;
}