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204. Count Primes
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204. Count Primes
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/*
Count the number of prime numbers less than a non-negative number, n.
Example:
Input: 10
Output: 4
Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7.
*/
public class Solution {
public int CountPrimes(int n) {
List<int> li=new List<int>();
bool success;
for(int i=2;i<n;i++){
success=EitherPrime(i);
if(success){
li.Add(i);
}
}
bool EitherPrime(int num){
int count=0;
if(num==2){
count=0;
}
else if(num%2==0){
count=1;
}
else if(num==3){
count=0;
}
else if(num%3==0){
count=1;
}
else{
for(int i=5;i<=Math.Sqrt(num);i=i+2){
if(num%i==0){
count++;
}
if(count>0){
break;
}
}
}
if(count==0){
return true;
}
else{
return false;
}}
return li.Count();
}
}