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Bitwise and (or &) of a range in C++
In this problem, we are given two integer values a and b. And our task is to find the bitwise and (&) of range from a to b. This means we will have to find the value of a & a+1 & a+2 & … b-1 & b.
Let’s take an example to understand the problem,
Input − a = 3 , b = 8
Output − 0
Explanation − 3 & 4 & 5 & 6 & 7 & 8 = 0
To solve the problem, a simple solution is starting from a and find bitwise and of all numbers by increasing one to b.
More effective Solution,
This is a more effective solution, this can be done using −
Step1 − Flip LSB of b.
Step2 − Compare the number with a and b, check if it is in range,
Step 2.1 − if the number is greater than a flip its LSB gain.
Step 2.2 − if it is not greater than a then number = result.
Now, let’s see the algorithm above in working −
Example − a = 3 and b = 8.
Solution −
Step1 − b = 8 (1000), flipping LSB which is the only one in the number. The number becomes 0000 i.e. 0
Step2 − 0 is less than 3, 0 is the result.
Example
Now, let’s see the code to solve the problem,
#include <stdio.h>
int main(){
long a, b;
a = 3; b = 8;
do{
b -= (b & -b);
}while(a < b);
printf("%li", b);
}Output
0
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