204. Count Primes #
题目 #
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.
题目大意 #
统计所有小于非负整数 n 的质数的数量。
解题思路 #
- 给出一个数字 n，要求输出小于 n 的所有素数的个数总和。简单题。
代码 #
package leetcode
func countPrimes(n int) int {
isNotPrime := make([]bool, n)
for i := 2; i*i < n; i++ {
if isNotPrime[i] {
continue
}
for j := i * i; j < n; j = j + i {
isNotPrime[j] = true
}
}
count := 0
for i := 2; i < n; i++ {
if !isNotPrime[i] {
count++
}
}
return count
}