LeetcodeCount Primes
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题目链接:https://leetcode.com/problems/count-primes/
题目:
Description:
Count the number of prime numbers less than a non-negative number, n.
思路:
埃拉托色尼选筛法
算法:
public int countPrimes(int n) { boolean c[] = new boolean[n]; for (int i = 2; i * i < n; i++) { if(!c[i]){ for (int j = i+i; j < n; j += i) { if(!c[j]) c[j] = true; } } } int count = 0; for (int i = 2; i < n; i++) { if (!c[i]) count++; } return count; }
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