Summary of the use of bit operations

Preface

In order to improve efficiency when brushing Leetcode, many operations can be optimized using bit operations. This article is used to collect and summarize the related operations of bit operations. The basic knowledge of bit operations can be seen: the portal .

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Realize the four arithmetic

This is too hard core, and look on the line, and if writing code so that it would be too exaggerated !! Fight (O ^- ) ~ '' ☆ ☆ ミ ミ

Plus one operation

Conventional code:

int a = 1;
a += 1;

Bit operation code:

int a = 1;
a = -~a;

Minus one operation

int a = 1;
a -= 1;

Bit operation code:

int a = 1;
a = ~-a;

Multiply by 2 operation

This operation can be performed as long as it is multiplied by the power of 2, and it is shifted to the left as much as the power of 2 is multiplied.
Conventional code:

b = a * 2;

Bit operation code:

b = a << 1;

Multiply by 2 and add 1 operation

Conventional code:

b = a * 2 + 1;

Bit operation code:

b = a << 1 | 1;

Divide by 2 operation

This operation can be performed as long as it is divided by the power of 2, and it is shifted to the right as much as the power of 2 is divided.
Conventional code:

b = a / 2;

Bit operation code:

b = a >> 1;

Remainder (modulo) operation

Note: The divisor must be a power of 2.

Conventional code:

a = a % 4;

Bit operation code:

a = a & (4 - 1);

Determine parity

Conventional code:

if(a % 2);//奇数

if(!(a % 2));//偶数

Bit operation code:

if(a & 1);//奇数

if(!(a & 1));//偶数

Swap two numbers

Conventional code:

int a = 1,b = 2,temp;
temp = a;
a = b;
b = temp;

Bit operation code:

int a = 1,b = 2;
a ^= b;
b ^= a;
a ^= b;

Case conversion

In fact, this is not magic!

Use or operation |and to 空格convert English characters to lowercase

('a' | ' ') = 'a';
('A' | ' ') = 'a';

Use the AND operation &and to 下划线convert English characters to uppercase

('b' & '_') = 'B'
('B' & '_') = 'B'

Using the XOR operation ^, and 空格for English characters invert case

('d' ^ ' ') = 'D'
('D' ^ ' ') = 'd'

XOR

XOR (^)

• If we do the ^ operation on 0 and binary, we still get this binary bit.
  $0⨁0=0,0⨁1=1$
• If we do the ^ operation on the same binary, the result returned is 0
  $1⨁1=0,a⨁a=0(a$ can be any number$)$
• ^Satisfy the commutative and associative laws
  $a⨁b⨁a=(a⨁a)⨁b=0⨁b=b$
  Related leetcode topics:
  136. The number that appears only once
  389. Find the difference

data

Bit arithmetic means multiply by 2 and multiply by 2+1
algorithm articles: Basic
bit arithmetic operations Bit Twiddling Hacks

postscript

Continually updated!