Leetcode-204 Count Primes

#204 Count Primes

Count the number of prime numbers less than a non-negative number, n.

题解：这道题如果对每个小于n的数都进行判断是否为素数并计数会超时，因此采用筛法来解这题。建一个数组，从2开始, 把其倍数小于N的都删掉。

class Solution {
public:int countPrimes(int n) {vector<int>arr(n,1);int sum=0;for(int i=2;i<=n;i++){if(arr[i]==1){sum++;for(int j=i;j<n;j+=i){arr[j]=0;}}}return sum;}
};

转载于:https://www.cnblogs.com/fengxw/p/6061597.html

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