204. Count Primes

Count the number of prime numbers less than a non-negative number, 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 * 106

# @lc code=start
using LeetCode

function count_primes(n::Int)
    if n <= 1
        return 0
    end
    arr = fill(true, n - 1)
    for i in 2 : n - 1
        for j in i ^ 2 : i : (n - 1)
            arr[j] = false
        end
    end
    return sum(arr) - 1
end
# @lc code=end

count_primes (generic function with 1 method)

This page was generated using DemoCards.jl and Literate.jl.