I'm trying to write a program that counts the number of primes in a given interval
I came up with this:
def check_primes(numb):
if numb == 2 :
return True
n = 2
while n < numb:
if numb % n != 0:
return True
else:
return False
def count_primes(num) :
count = 0
for m in range(2,num) :
if check_primes(m) == True :
count += 1
return count
but when I try count_primes(100) I get 50 instead of 25, for some reason. Can anyone explain to me what's wrong in there?
In your while, you are not increasing n. Your method runs for just n=2 and that's it.
So, just add n += 1 to your while:
def check_primes(numb):
if numb == 2 :
return True
n = 2
while n < (numb // 2) + 1:
if numb % n != 0:
n += 1
else:
return False
return True
Also note that there is not need to check all numbers to numb. You can do check it till numb/2 and that would be enough.
Related
I have been coding this problem for HackerRank and I ran into so many problems. The problem is called "Plus Minus" and I am doing it in Python 3. The directions are on https://www.hackerrank.com/challenges/plus-minus/problem. I tried so many things and it says that "there is no response on stdout". I guess a none-type is being returned. Here is the code.:
def plusMinus(arr):
p = 0
neg = 0
z = arr.count(0)
no = 0
for num in range(n):
if arr[num] < 0:
neg+=1
if arr[num] > 0:
p+=1
else:
no += 1
continue
return p/n
The following are the issues:
1) variable n, which represents length of the array, needs to be passed to the function plusMinus
2) No need to maintain the extra variable no, as you have already calculated the zero count. Therefore, we can eliminate the extra else condition.
3) No need to use continue statement, as there is no code after the statement.
4) The function needs to print the values instead of returning.
Have a look at the following code with proper naming of variables for easy understanding:
def plusMinus(arr, n):
positive_count = 0
negative_count = 0
zero_count = arr.count(0)
for num in range(n):
if arr[num] < 0:
negative_count += 1
if arr[num] > 0:
positive_count += 1
print(positive_count/n)
print(negative_count/n)
print(zero_count/n)
if __name__ == '__main__':
n = int(input())
arr = list(map(int, input().rstrip().split()))
plusMinus(arr, n)
The 6 decimals at the end are needed too :
Positive_Values = 0
Zeros = 0
Negative_Values = 0
n = int(input())
array = list(map(int,input().split()))
if len(array) != n:
print(f"Error, the list only has {len(array)} numbers out of {n}")
else:
for i in range(0,n):
if array[i] == 0:
Zeros +=1
elif array[i] > 0:
Positive_Values += 1
else:
Negative_Values += 1
Proportion_Positive_Values = Positive_Values / n
Proportion_Of_Zeros = Zeros / n
Proportion_Negative_Values = Negative_Values / n
print('{:.6f}'.format(Proportion_Positive_Values))
print('{:.6f}'.format(Proportion_Negative_Values))
print('{:.6f}'.format(Proportion_Of_Zeros))
I try to find out the index of a certain Fibonacci number. However my program returned to me this result "Your program took too long to execute. Check your code for infinite loops, or extra input requests" after typing in 1134903171.
num = 1
num_prev = 1
n = int(input())
i = 1
if n < 2:
print(1, 2)
else:
while i <= n + 2:
num_prev, num = num, num + num_prev
i += 1
if n == num:
print(i + 1)
break
elif i == n + 3:
print(-1)
#break`
Thank you guys. The problem of last code is that: if the number isn't a Fibonacci number and meanwhile it is too large, it will took to many loops for the calculation. As I used a web compiler to calculate, they do not allow such "infinity" loop to operate. Then I used a math methode to limite the loop.
import math
N=int(input())
root1=math.sqrt(5*N*N+4)
root2=math.sqrt(5*N*N-4)
i=1
num, num_prev = 1, 1
if root1%1==0 or root2%1==0:
while i <= N+2:
num_prev,num = num,(num+num_prev)
i+=1
if N==num:
print(i+1)
break
else:
print(-1)
But the best answer could be:
prev, next = 1, 1
index = 2
possible_fib = int(input())
while possible_fib > next:
prev, next = next, prev + next
index += 1
if possible_fib == next:
print(index)
else:
print(-1)
This code is to convert decimals to binary.
What I'm trying to do is to chop off the decimal part after diving by 2.
binary = []
n = 25
while n != 0:
binary.append(n % 2)
n = n / 2
int(n) #this part
print(binary)
print(n)
choose = input("continue?[Y/N]")
if choose == 'y':
continue
else:
break
print(list(reversed(binary)))
Is this what you want?
binary = []
n = 25
while n != 0:
binary.append(n % 2)
n = n / 2
n = int(n) #assign result to n
print(binary)
print(n)
choose = input("continue?[Y/N]")
if choose == 'y':
continue
else:
break
print(list(reversed(binary)))
I have created the below script to find out the prime factors of a number :
def check_if_no_is_prime(n):
if n <= 3:
return True
else:
limit = int(math.sqrt(n))
for i in range(2,limit + 1):
if n % i == 0:
return False
return True
def find_prime_factors(x):
prime_factors = []
if check_if_no_is_prime(x):
prime_factors.append(1)
prime_factors.append(x)
else:
while x % 2 == 0 and x > 1:
prime_factors.append(2)
x = x // 2
for i in range(3,x+1,2):
while x % i == 0 and x > 1:
if check_if_no_is_prime(i):
prime_factors.append(i)
x = x // i
if x <= 1:
return prime_factors
return prime_factors
no = int(input())
check = find_prime_factors(no)
print (check)
I am not sure whether this is the best and efficient way to do this ?
Can someone please point out any better way to do this ?
using sieve of erathnostanes to get all prime numbers from 2 to whatever limit inputted
def sieve(N):
from math import floor,sqrt
A=[1 for x in range(N+1)]
for count in range(2):
A[count]=0
for i in range(floor(sqrt(N))+1):
if A[i]==1:
for k in range(i*i,N+1,i):
A[k]=0
ans=list(enumerate(A))
res=[]
for (i,j) in ans:
if j==1:
res+=[i]
return res
print(sieve(100))
#my code
def primetest(x):
if x < 2:
return False
if x == 2:
return True
if x % 2 == 0:
return False
for i in range(3,(x**0.5)+1):
if x % i == 0:
return False
return True
def nthprime(n):
primes = []
x = 2
while len(primes) < n:
if primetest(x) == True:
primes.append(x)
x = x + 1
return list(-1)
print nthprime(10001)
Whenever I try to run this it says that "print nthprime(10001)" is invalid syntax.
-prime test is to test wether a number is prime and nthprime creates a list of prime numbers a certain lengths and then return the last element of the list.
print is a function in Python 3, not a statement. You should change your last line of code to:
print(nthprime(10001))
In your code:
def nthprime(n):
primes = []
x = 2
while len(primes) < n:
if primetest(x) == True:
primes.append(x)
x = x + 1
return list(-1) // this is the error
I think you meant primes[-1], like this:
def nthprime(n):
primes = []
x = 2
while len(primes) < n:
if primetest(x) == True:
primes.append(x)
x = x + 1
return primes[-1] // this is now correct
You're also going to need to specify a range in integers, not float. So this:
for i in range(3,(x**0.5)+1):
Becomes this:
for i in range(3,int((x**0.5)+1)): // note the "int"