How to extract ‘k’ least significant bits from a number
Problem statement
Given n and k, extract the k least significant bits of n. Return -1 if k is larger than the number of bits used to represent n.
Example 1
- Input:
n=11,k=2 - Output:
11
The binary representation of 11 is 1011, and we extract the 2 LSBs as 11.
Example 2
- Input:
n=14,k=5 - Output:
-1
The binary representation of 14 is 1110. Only 4 bits are used in the binary representation of 14 and the ask is for 5. Therefore, we return -1.
Solution
- Convert the decimal value to binary form.
- Take the last
kcharacters from the result of the first step.
Code example
Let’s look at the code below:
public class Main{public static void main(String[] args) {int num=8;int k=3;String binaryForm = Integer.toBinaryString(num);if(k > binaryForm.length()) System.out.println("-1");else System.out.println(binaryForm.substring(binaryForm.length() - k));}}
Code explanation
- Line 4: We define
num. - Line 5: We define
k. - Line 6: We convert
numto binary form using thetoBinaryString()method of theIntegerclass. - Lines 7 to 8: If the value of
kis greater than the length of the binary string obtained in line 6, we print-1. Otherwise, we print the substring from the index of the difference of the length of the binary string andkto the end of the binary string.
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