check if number is power of 2 pythoncheck if number is power of 2 python

As noted above, for some numbers these functions are not accurate and actually give FALSE RESULTS: This is because math functions use floats, and those have an inherent accuracy problem. For instance, on AArch64 it usually takes 4 instructions: It may not be fast or short, but it's correct unlike the top answers. I love popcount but for the power-of-2 test, the test. How do I easily find whether or not a number is a power of two? Python Server Side Programming Programming. Release my children from my debts at the time of my death, Line-breaking equations in a tabular environment. Given an integer n, return true if it is a power of two. Contribute to the GeeksforGeeks community and help create better learning resources for all. The former approach is more human-friendly but generally less efficient; the latter approach is more machine-friendly but generally more efficient. Is it better to use swiss pass or rent a car? Using robocopy on windows led to infinite subfolder duplication via a stray shortcut file. How can I avoid this? (x == 0) && ! Please see Count set bits in an integer for counting set bits.4. ln(1<<29) / ln(2) comes out to 29.000000000000004. @will., you're right. Is it better to use swiss pass or rent a car? Example: Number = 8 Making statements based on opinion; back them up with references or personal experience. The time complexity of this method would be O ( log2N ). @CallMeStag makes sense but to say like that 1 is power of all number, The only reason I have added the answer is that when I was solving this wonderful obsessive problem of whether or not a given number is the power of two then I found. If you look at the binary values of all powers of 2, you can see that there is only one bit True. Refer to the excellent and detailed answer to "How to check if a number is a power of 2" for C#. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Line integral on implicit region that can't easily be transformed to parametric region. All power of two numbers have only one bit set. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. That's why you had an infinite loop. Examples: Input : 4 Output : Yes 2 2 = 4 Input : 12 Output : No Recommended: Please try your approach on {IDE} first, before moving on to the solution. This is the bit-shift method in T-SQL (SQL Server): It is a lot faster than doing a logarithm four times (first set to get decimal result, 2nd set to get integer set & compare). So I would do something like this: This works since binary is based on powers of two. Why the ant on rubber rope paradox does not work in our universe or de Sitter universe? Why would God condemn all and only those that don't believe in God? is absolutely continuous? C++ and Java are different languages and each offers different facilities. By using our site, you How to find the power required to 2 for a known value in Python, While loop doesn't stop when number is power of 2. Not the answer you're looking for? Using robocopy on windows led to infinite subfolder duplication via a stray shortcut file. How can I avoid this? Alternatively though, i would go with something like this: While this does not directly answer your question, the fastest way to implement this would be. Seriously, how did you just get 120 rep for a demonstrably wrong answer? (which of course would probably take longer and use more memory, since your python interpreter will have to interpret python instead of just converting your integer to a string in C, but this is about algorithmic principles, right?) So the input looks something like this: 13, 8 first number being x second number being n. You may well have to use a "close enough" comparison. How many alchemical items can I create per day with Alchemist Dedication? After the last possible division, if the value of the number is equal to 1, it is a power of 2. When laying trominos on an 8x8, where must the empty square be? Binary representation of any power of 2 number, has always only one bit set, other bits are always zero. "\$\endgroup\$ - Martin Smith. 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. Thanks for contributing an answer to Stack Overflow! 10 . Below is the implementation of this method. Line integral on implicit region that can't easily be transformed to parametric region, How to form the IV and Additional Data for TLS when encrypting the plaintext. Approach 1: Taking the log of the given number on base 2 to get the power Example Live Demo # power of 2 def find(n): if (n == 0): return False while (n != 1): if (n % 2 != 0): return False n = n // 2 return True # Driver code if(find(98)): print('Yes') else: print('No') Output No Approach 2: Using the logical statements Example Live Demo Any subtle differences in "you don't let great guys get away" vs "go away"? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. To solve this, we will follow these steps if n is same as 0, then return False We have to check whether there exists any subset of the nums whose bitwise AND is a power of two or not. While this code may solve the question, I am not a professional. Without using libraries and other methods just loops and .push. 8 Answers. All power of two numbers has only a one-bit set. Improving time to first byte: Q&A with Dana Lawson of Netlify, What its like to be on the Python Steering Council (Ep. Python 2: It gets complicated for Python 2. 592) Featured on Meta Colors update: A more detailed look. Instead, I store all the powers of 2 in a set beforehand, in order to check a given input in O(1). Can somebody be charged for having another person physically assault someone for them? US Treasuries, explanation of numbers listed in IBKR. A course question was to define a function using a while loop (and without using the math function) that determines if a parameter is a power of 2. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. A better choice is to take the log of the number. The binary representation of every number and the (number-1) share at least a single 1 bit, except if the number is a power of two. So when subtracting 1 from it, that bit flips to 0 and all preceding bits flip to 1. And then to see if the number is a regular integer (and not a floating point), just check if the remainder is 0 by . @wim, that's another possibility but it introduced other problems such as, +1 very good. 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To subscribe to this RSS feed, copy and paste this URL into your RSS reader. First, assuming you have a specific logarithm operator (many languages provide logarithms to base 10 or base e only), logab can be calculated as logxb / logxa (where x is obviously a base that your language provides). Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Example 1: Input: n = 1 Output: true Explanation: 2 0 = 1 Example 2: Input: n = 16 Output: true Explanation: 2 4 = 16 Example 3: Input: n = 3 Output: false Constraints: That's the logic in this program. def is_power_of_two(number : int) -> bool: while number != 1: if number % 2: return False number /= 2 return True . Top 10 largest Powerball jackpots. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. How did this hand from the 2008 WSOP eliminate Scott Montgomery? How can this be improved? Time complexity: O(log N)Auxiliary Space: O(1), If we subtract a power of 2 numbers by 1 then all unset bits after the only set bit become set; and the set bit becomes unset.For example for 4 ( 100) and 16(10000), we get the following after subtracting 13 > 01115 > 01111. Generalise a logarithmic integral related to Zeta function. It would work if you were using from __future__ import division, which changes the behaviour of / - but this changes its behaviour throughout the program, which may not be what you want. Can consciousness simply be a brute fact connected to some physical processes that dont need explanation? One approach would be to use bit manipulations: Explanation: every power of 2 has exactly 1 bit set to 1 (the bit in that number's log base-2 index). To check if a given number is a power of 2, we can continuously divide the number by 2, on the condition that the given number is even. What's the translation of a "soundalike" in French? Note that there is always exactly 1 bit set. python3 function to check if parameter is a power of 2 with a while loop and without using math function, How to express a power of 2 as a recursive function. Can a creature that "loses indestructible until end of turn" gain indestructible later that turn? You may want a > 0 test if you're using signed integers. (x & (x - 1)); Will work fine; one less than a power of two is all 1s in the less significant bits, so must AND to 0 bitwise. Bit manipulations are simple operations, not calling any functions. How can I calculate whether one number is a power of another number? Thanks for contributing an answer to Stack Overflow! Do the subject and object have to agree in number? I'm trying to find whether a number is a power of 2 using recursion. Most of the above answers use bin() of format(int(input()), "b"), The below code also works: Ev(x) returns True if x is power of 2, The above code is based on generating bin(), I have tried to add my answer because I found what we are doing using bin(x)[3:] or format(x, "b") is almost like asking the boolean answer of whether or not a given number x is divisible by two..and we keep asking the same. You're also missing a test for negative value of x. Neat, how did you edit it without the 'edited x minutes ago' appearing? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Is there a word in English to describe instances where a melody is sung by multiple singers/voices? What is the best way to determine if a given number is a power of two? To write a program to check if an integer is a power of two, you could follow two basic strategies: check the number based on its decimal value, or check it based on its binary representation. Tomerikoo's answer is very well explained and thought-out. To take the log of a number, we use the math module log () function. Given a positive integer, write a function to find if it is a power of two or not.Examples : 1. If Phileas Fogg had a clock that showed the exact date and time, why didn't he realize that he had reached a day early? rev2023.7.24.43543. answer to "How to check if a number is a power of 2", Improving time to first byte: Q&A with Dana Lawson of Netlify, What its like to be on the Python Steering Council (Ep. This was my solution for a function which checks which number is a base of another: Late to the party, though yet, another way: Thanks for contributing an answer to Stack Overflow! Check if a number can be represented in the form of pow (a, b) (a^b). I don't think there is any possible faster methods. @Mike F: Indeed, it does seem people will vote on answers without checking them. Check if a number is a power of 4 or not Practice this problem Approach 1 A simple solution is to calculate log 4 n for a given number n. If it returns an integral value, then we can say that the number is a power of four. Input is not supposed to be initially stored in a variable. however, with from __future__ import division the outputs change to the correct (or at least more intuitive) results - to get the original integer math behaviour you need to use // instead (as in python3). To summarize briefly the answer cited above: The first term, before the logical and operator, simply checks if n isn't 0 and hence not a power of 2. Use *2 instead of bit shifts. check if number is power of 2 python. 1. What is the smallest audience for a communication that has been deemed capable of defamation? Bitwise AND the number with its just previous number should be equal to ZERO. Using robocopy on windows led to infinite subfolder duplication via a stray shortcut file. How can I avoid this. So when subtracting 1 from it, that bit flips to 0 and all preceding bits flip to 1. def is_power_of (number, base): # Base case: when number is smaller than base. 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. So you could just count the binary 1s in your int's binary representation: would also work. Example : 4 can be represented as (2^2 ) , (4 & 3)=0 or in binary (100 & 011=0), Time Complexity: O(1)Auxiliary Space: O(1). Here are the Top 10 jackpots since the Powerball lottery began in 1992: $2.04 billion, Nov. 7, 2022: Won in California. Binary of 8: 1 0 0 0 Improving time to first byte: Q&A with Dana Lawson of Netlify, What its like to be on the Python Steering Council (Ep. @CassioNeri Your hack doesn't work. Looking for story about robots replacing actors. excellent answer, and definitely a better approach than OPs, so well worthy of upvoting :) Only thing is that when using the, @MarcusMller I don't agree with rolling it all into that, Finding if a number is a power of 2 using recursion, Improving time to first byte: Q&A with Dana Lawson of Netlify, What its like to be on the Python Steering Council (Ep. The implementation can be seen below in C++, Java, and Python: C++ Java Python Download Run Code Output: 32768 is a power of 8 Initially, as long as is even and greater than zero, it means there's a zero at the end of the binary representation of . Check your tickets to see if you won the Mega Millions $720 million jackpot. At time of commenting they were all bugged. What are some compounds that do fluorescence but not phosphorescence, phosphorescence but not fluorescence, and do both? Is it better to use swiss pass or rent a car? To handle this case also, our expression will become n& (!n&(n-1)) (thanks to https://www.geeksforgeeks.org/program-to-find-whether-a-no-is-power-of-two/Mohammad for adding this case). So the correct answer will be more like this: You need to test your code works on several test cases, not just ones for which you want particular results. Python goes one better since it can work out the logarithm for an arbitrary base without that tricky equality above. you can use to check if a number is a power of two and for sure not the most Another solution is to keep dividing the number by two, i.e, do n = n/2 iteratively. This approach is demonstrated below in C++, Java, and Python: C++ Java Python 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 My bechamel takes over an hour to thicken, what am I doing wrong. (A modification to) Jon Prez Laraudogoitas "Beautiful Supertask" time-translation invariance holds but energy conservation fails? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. A number in the power of two if it has only one set bit in the binary representation. You're right, if you have the POPCNT instruction on your CPU it's faster. How can I calculate whether one number is a power of another number? 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. Share your suggestions to enhance the article. Use some sort of input stream to get the number. In this case, we divide by two to shift the binary representation to the right (remove the trailing zero). C++ Java C# Javascript Python3 C #include <iostream> using namespace std; #include<math.h> int main () { int b = 81; int a = 3; double p = log10(b) / log10(a); if (p - (int)p == 0) { cout<<"YES"; } else{ cout<<"NO"; } return 0; } Output YES Making statements based on opinion; back them up with references or personal experience. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Copyright Tutorials Point (India) Private Limited. Top 10 largest Powerball jackpots. Not the answer you're looking for? It only uses a POPCNT cpu instruction and one comparison. Connect and share knowledge within a single location that is structured and easy to search. So I'd start with the following code, now with added edge-case detection: See for example the following complete program which shows this in action: If you're the sort that's worried about floating point operations, you can do it with repeated multiplications but you should test the performance of such a solution since it's likely to be substantially slower in software than it is in hardware. You can actually use ECMAScript5 Math.log: Remember, in math, to get a logarithm with an arbitrary base, you can just divide log10 of the operand (x in this case) by log10 of the base. To learn more, see our tips on writing great answers. Any subtle differences in "you don't let great guys get away" vs "go away"? To learn more, see our tips on writing great answers. Check if a number is a perfect power of another number, binary search to see if a number a power of 2. To handle this case also, our expression will become n& (!n&(n-1)) (thanks to https://www.geeksforgeeks.org/program-to-find-whether-a-no-is-power-of-two/Mohammad for adding this case). Conclusions from title-drafting and question-content assistance experiments How can we decide that an integer is power of 2 by using bit manipulation? Each player selects five numbers from 1 to 70 for the white balls and one number from 1 to 25 for the Mega Ball . you might want to fix the infinite loop case with something like. Here's a constant-time solution that handles every special case mentioned in the comments so far: I think I have a nice simple way of doing it (without calling a library) recursively: >>>(math.log(int(num),int(base))).is_integer(), This will return a boolean value either true or false. My bechamel takes over an hour to thicken, what am I doing wrong. What happens if sealant residues are not cleaned systematically on tubeless tires used for commuters? Let's see one example of a number that contains only one set bit. Not the answer you're looking for? Please see Count set bits in an integer for counting set bits. Otherwise, return false. A power of two will have just one bit set (for unsigned numbers). Who counts as pupils or as a student in Germany? A very simple solution could go like this: I'll leave it to the OP to decide if he wants to apply the trivial fix or rewrite his requirements. Find centralized, trusted content and collaborate around the technologies you use most. Check whether a given number is a power of two, Is this mold/mildew?