Leetcode:count Primes

Description:

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

Ideas

A prime number cannot be divisible by an integer smaller than it, and a Boolean array, starting with 2, is deleted with multiples of less than N.

Note that the inner loop starts with I, and smaller than I will be previously check.

[CODE]

public class Solution {public    int countprimes (int n) {     //2,3,5,7,11,13,17      //20  5     //init Check  n     boolean[] A = new boolean[n];     for (int i=2, i*i<n; i++) {        if (!a[i]) {for            (int j=i; i*j<n; J + +) {                A[i*j] = true;            }        }     }     int c=0;          for (int i=2; i<n; i++) {         if (a[i] = = False) ++c;     }     return c;    }}

Leetcode:count Primes