Given an unsigned integer, reverse all bits of it and return the number with reversed bits.
Input : n = 1 Output : 2147483648 On a machine with size of unsigned bit as 32. Reverse of 0....001 is 100....0. Input : n = 2147483648 Output : 1
In the previous post we had seen two method that solved this problem in O(n) & O(logn ) time. Here we solve this problem in O(1) time using lookup table. It’s hard to reverse all 32 bits (assuming this as size of int) in one go using lookup table (” because it’s infeasible to create lookup table of size 232-1 “). So we break 32 bits into 8 bits of chunks( lookup table of size 28-1 “0-255”).
in lookup tale we will store reverse of every number that are in a range( 0-255)
LookupTable = 0 | binary 00000000 Reverse 00000000
LookupTable = 128 | binary 00000001 reverse 10000000
LookupTable = 64 | binary 00000010 reverse 01000000
LookupTanle = 192 | binary 00000011 reverse 11000000
LookupTable = 32 | binary 00000100 reverse 00100000
and so on… upto lookuptable.
Let’s take an Example How lookup table work.
let number = 12456
in Binary = 00000000000000000011000010101000
Split it into 8 bits chunks : 00000000 | 00000000 | 00110000 | 10101000 in decimal : 0 0 48 168 reverse each chunks using lookup table : Lookuptable[ 0 ] = 0 | in binary 00000000 Lookuptable[48 ] = 12 | in binary 00001100 Lookuptable = 21 | in binary 00010101 Now Binary : 00000000 | 00000000 | 00001100 | 00010101 Binary chunks after rearrangement : 00010101 | 00001100 | 00000000 | 00000000 Reverse of 12456 is 353107968
Time complexity :O(1)
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- Write an Efficient C Program to Reverse Bits of a Number
- Count set bits in an integer
- Count number of bits to be flipped to convert A to B
- Rotate bits of a number
- Next higher number with same number of set bits
- Program to count number of set bits in an (big) array
- Count total set bits in all numbers from 1 to n
- Swap bits in a given number
- Swap all odd and even bits
- Toggle all the bits of a number except k-th bit.
- Copy set bits in a range
- Print first n numbers with exactly two set bits
- Check if bits of a number has count of consecutive set bits in increasing order
- Check if a number has bits in alternate pattern | Set 1
- Count minimum bits to flip such that XOR of A and B equal to C
- Count trailing zero bits using lookup table
- Count all pairs of an array which differ in K bits
- Change bits to make specific OR value
- How to swap two bits in a given integer?
- Reverse an array without using subtract sign ‘-‘ anywhere in the code
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