How can i check bits from MST

#1

how can i check bits from MST as we can only get last bit from a&1

#2

hello @sreejan123
to find position of required msb.
compute xor of the two given range.
and then use loop to find its last set bit.
image

#3

cant understand how second loop is working

#4

let say u have found msb at position 5.
then that loop is calculating 11111 (in binary) this value.

it is just keep on adding 2^i in ur answer (where i will from 0 to pos-1)

#5

thanks but in hint video it is more complicated and totally different from your answer

#6

no it is not complicated.
the logic that i explained is the only optimal solution

#7

okay so main logic is we have to make all bits 0 except mst ?

#8

sorry 1 except 1st bit

#9

yeah ,
An efficient solution is to consider pattern of binary values from L to R. We can see that first bit from L to R either changes from 0 to 1 or it stays 1 i.e. if we take the XOR of any two numbers for maximum value their first bit will be fixed which will be same as first bit of XOR of L and R itself.
After observing the technique to get first bit, we can see that if we XOR L and R, the most significant bit of this XOR will tell us the maximum value we can achieve i.e. let XOR of L and R is 1xxx where x can be 0 or 1 then maximum XOR value we can get is 1111 because from L to R we have all possible combination of xxx and it is always possible to choose these bits in such a way from two numbers such that their XOR becomes all 1. It is explained below with some examples,

Examples 1:
L = 8 R = 20
L ^ R = (01000) ^ (10100) = (11100)
Now as L ^ R is of form (1xxxx) we
can get maximum XOR as (11111) by
choosing A and B as 15 and 16 (01111
and 10000)

Examples 2:
L = 16 R = 20
L ^ R = (10000) ^ (10100) = (00100)
Now as L ^ R is of form (1xx) we can
get maximum xor as (111) by choosing
A and B as 19 and 20 (10011 and 10100)
So the solution of this problem depends on the value of (L ^ R) only. We will calculate the L^R value first and then from most significant bit of this value, we will add all 1s to get the final result.

#10

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