Count Primes
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题目:
Count the number of prime numbers less than a non-negative number, n.
解题思路:
思路一(Time limit Exceed):
class Solution:
# @param {integer} n
# @return {integer}
def countPrimes(self, n):
import math
numbers = 2
for i in range(5,n):
Flag = True
for j in range(2,int(math.sqrt(i))+1):
if i%j==0:
Flag = False
break
if Flag:
numbers += 1
return numbers
思路2(accept):
class Solution:
# @param {integer} n
# @return {integer}
def countPrimes(self, n):
from math import *
primes = []
numbers = 0
if n<=2:
return 0
for i in range(n):
primes.append(True)
j = 2
while j<=sqrt(n-1):
if primes[j]:
k= 2*j
while k<n:
primes[k]=False
k = k+j
j += 1
for i in range(2,n):
if primes[i]:
numbers += 1
return numbers
总结:
本题不难,只是在一些python的特性上纠结不清
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