Rotate bits of a number 左旋转或右旋转一个数 @GFG

最新推荐文章于 2025-06-06 15:01:27 发布

原创最新推荐文章于 2025-06-06 15:01:27 发布 · 2.1k 阅读

1 ·

CC 4.0 BY-SA版权

GeeksForGeeks 专栏收录该内容

32 篇文章

订阅专栏

本文详细解释了位旋转的概念，包括左旋转和右旋转，通过示例展示了如何在不同位数下进行位旋转操作，并提供了相应的Java代码实现。

Bit Rotation: A rotation (or circular shift) is an operation similar to shift except that the bits that fall off at one end are put back to the other end.

In left rotation, the bits that fall off at left end are put back at right end.

In right rotation, the bits that fall off at right end are put back at left end.

Example:
Let n is stored using 8 bits. Left rotation of n = 11100101 by 3 makes n = 00101111 (Left shifted by 3 and first 3 bits are put back in last ). If n is stored using 16 bits or 32 bits then left rotation of n (000…11100101) becomes 00..0011100101000.
Right rotation of n = 11100101 by 3 makes n = 10111100 (Right shifted by 3 and last 3 bits are put back in first ) if n is stored using 8 bits. If n is stored using 16 bits or 32 bits then right rotation of n (000…11100101) by 3 becomes 101000..0011100.

/**
 *
 * 左旋转：shift掉左边的bits，补到右边
      右旋转：shift掉右边的bits，补到左边

	例如： 1110 0101 左旋转3个数变成 0010 1111
              1110 0101 右旋转3个数变成 1011 1100
 *
 */
public class RotateBitsOfANumber {

	public static void main(String[] args) {
		int n = 0xE5;		// 1110 0101
		int d = 3;
		int int_bits = 8;
		
		System.out.println(Integer.toBinaryString(leftRotate(n, d, int_bits)));	//0010 1111
		System.out.println(Integer.toBinaryString(rightRotate(n, d, int_bits)));	//1011 1100
	}

	// 最后一个&是用来保持int_bits位数
	public static int leftRotate(int n, int d, int int_bits){
		return ((n<<d) | (n >> (int_bits-d))) & ((1<<int_bits)-1);
	}
	
	public static int rightRotate(int n, int d, int int_bits){
		return ((n>>d) | (n << (int_bits-d))) & ((1<<int_bits)-1);
	}
	
}

#include<stdio.h>
#define INT_BITS 32
 
/*Function to left rotate n by d bits*/
int leftRotate(int n, unsigned int d)
{
   /* In n<<d, last d bits are 0. To put first 3 bits of n at 
     last, do bitwise or of n<<d with n >>(INT_BITS - d) */
   return (n << d)|(n >> (INT_BITS - d));
}
 
/*Function to right rotate n by d bits*/
int rightRotate(int n, unsigned int d)
{
   /* In n>>d, first d bits are 0. To put last 3 bits of at 
     first, do bitwise or of n>>d with n <<(INT_BITS - d) */
   return (n >> d)|(n << (INT_BITS - d));
}
 
/* Driver program to test above functions */
int main()
{
  int n = 16;
  int d = 2;
  printf("Left Rotation of %d by %d is ", n, d);
  printf("%d", leftRotate(n, d));
  printf("\nRight Rotation of %d by %d is ", n, d);
  printf("%d", rightRotate(n, d));
  getchar();
}

Ref:http://www.geeksforgeeks.org/rotate-bits-of-an-integer/