H面试程序（9）： 左旋字符串

 

题目：定义字符串的左旋转操作：把字符串前面的若干个字符移动到字符串的尾部。 

如把字符串abcdef左旋转2位得到字符串cdefab。 

请实现字符串左旋转的函数。要求时间对长度为n的字符串操作的复杂度为O(n)，辅助内存为O(1)。 

 

 

#include<stdio.h>
#include<iostream.h>

void swap(char & a, char &b)
{     
	  char temp;
      temp = a;
      a = b;
	  b =temp;
}
 
void reverse(char *s, int start, int  end )
{  
	int j = end,i =start;

	for( ; i<=(start+(end -start)/2);i++)
	{       
		    swap(s[i],s[j]);
			j--;
	}
    
}
void leftshift(char * s , int strlen, int num_leftshift) //通过三次翻转
{
   reverse(s, 0, num_leftshift-1);
   reverse(s, num_leftshift,strlen-1);
   reverse(s, 0,strlen-1 );
     
}

int main()
{
	char s[ ] = "little things make life beautiful!";
    cout<<"before leftshift the string is:"<<s<<endl;

	int strlen = sizeof(s)/sizeof(char)-1;
	int num_leftshift;
	printf("please input the number you want to leftshift:  ");
	scanf("%d",&num_leftshift);



	
	num_leftshift = num_leftshift%strlen;//允许翻转的位数大于字符串长度，做一个取余运算
	leftshift(s,strlen, num_leftshift );
	cout<<"after leftshift  the string is:"<<s<<endl;

	return 0;

}