"Leetcode-Interview algorithm classic-java Implementation" "204-count Primes (Statistical Prime)" __ Code

"204-count Primes (statistic prime numbers)" " leetcode-interview algorithm classic-java Implementation" "All topic Directory Index" code Download "Https://github.com/Wang-Jun-Chao" Original title

Description:
Count the number of prime numbers less than a non-negative number, N.
The main effect of the topic

Counts the number of primes less than the nonnegative integer n.
ideas for solving problems

Use See Eratosthenes-color sieve method.
Code Implementation

Algorithm implementation class

public class Solution {public

    int countprimes (int n) {

        if (n <= 1) {return
            0;
        }

        Default all element values are set to False
        boolean[] Notprime = new Boolean[n];
        Notprime[0] = true;
        Notprime[1] = true;

        for (int i = 2; I * i < n; i++) {
            //If I is a prime number, I set the multiple of I to a non prime number
            //If I is a composite number, then it must have been set to true because it is processed from 2
            if (!not Prime[i]) {for
                (int j = 2 * i; j < n; j + = i) {
                    notprime[j] = True
                ;

        }} Count the number of prime numbers
        int result = 0;
        For (Boolean b:notprime) {
            if (!b) {
                result++
            }}
        }

        return result;
    }

Evaluation Results

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