Leetcode•Apr 04, 2025
204. Count Primes
Hazrat Ali
Leetcode
Given an integer n, return the number of prime numbers that are strictly less than n.
Example 1:
Input: n = 10 Output: 4 Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7.
Example 2:
Input: n = 0 Output: 0
Example 3:
Input: n = 1 Output: 0
* Count Primes
*
* 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.
*/
Solution :
/**
* @param {number} n
* @return {number}
*/
const countPrimes = n => {
const isPrime = Array(n).fill(true);
let count = 0;
for (let i = 2; i < n; i++) {
if (isPrime[i]) {
count++;
for (let j = 2; i * j < n; j++) {
isPrime[i * j] = false;
}
}
}
return count;
};