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Java Solution for LeetCode algorithm problems, continually updating
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package g0201_0300.s0204_count_primes;
// #Medium #Top_Interview_Questions #Array #Math #Enumeration #Number_Theory
// #2022_06_28_Time_115_ms_(92.82%)_Space_46.8_MB_(85.39%)
public class Solution {
public int countPrimes(int n) {
boolean[] isprime = new boolean[n];
int count = 0;
for (int i = 2; i * i <= n; i++) {
if (!isprime[i]) {
for (int j = i * 2; j < n; j += i) {
isprime[j] = true;
}
}
}
for (int i = 2; i < isprime.length; i++) {
if (!isprime[i]) {
count++;
}
}
return count;
}
}