Problem
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
Constraints:
0 <= n <= 5 * 10^6
Solution
/**
* @param {number} n
* @return {number}
*/
var countPrimes = function(n) {
let seen = new Uint8Array(n), ans = 0
for (let num = 2; num < n; num++) {
if (seen[num]) continue
ans++
for (let mult = num * num; mult < n; mult += num)
seen[mult] = 1
}
return ans
};
Explain:
nope.
Complexity:
- Time complexity :
- Space complexity :