204. Count Prime Numbers | Count Primes

Count the number of prime numbers less than a non-negative number, n.

Example:

Input:10output:4explanation:there is 4 prime numbers less than, they is 2, 3, 5, 7.

Counts the number of all prime numbers that are less than nonnegative integer n .

Example:

Input: 10 Output: 4 Explanation: There are 4 of prime numbers less than 10, they are 2, 3, 5, 7.

424ms

1 classSolution {2Func CountPrimes (_ N:int)Int {3         ifN <2{return 0}4         //Screening Method5         varCount =06         //to create an array with default values7         varFlag = Array (repeating:false, Count:n)8         varVal:int =Int ()9          forIinch 2.. <NTen         { One             ifFlag[i] = =false A             { -Count + =1 -                 varJ:int =1 theval = j*I -                  while(true) -                 { -J + =1 +val = j*I -                     if(Val <N) +                     { AFlag[val] =true at                     } -                     Else -                     { -                          Break -                     } -                 } in             } -         } to         returnCount +     } -}

84ms

1 classSolution {2Func CountPrimes (_ N:int)Int {3Guard n >2 Else{return 0 }4         varSieve = [Bool] (repeating:true, Count:n)5         varCount = N/26         vari =37         8          whileI * I <N {9             ifSieve[i] {Ten                 varj = i *I One  A                  whileJ <N { -                     ifSieve[j] { -Count-=1  theSIEVE[J] =false -                     } -J + =2*I -                 } +             } -i + =2 +         } A          at         returnCount -     } -}

112ms

1 classSolution {2Func CountPrimes (_ N:int)Int {3Guard N >=3 Else{return 0 }4         varprimes = [Bool] (repeating:true, Count:n)5         varCount = n/26         vari =37          whileI <=Int (Double (n). SquareRoot ()) {8             ifPrimes[i] {9                 varj =ITen                  whileI*j <N { One                     ifprimes[i*J] { ACount-=1 -PRIMES[I*J] =false -                     } theJ + =2  -                 } -             } -i + =2  +         } -         returnCount +     } A}

204. Count Prime Numbers | Count Primes