hdu 2136 素数筛法

Problem Description Everybody knows any number can be combined by the prime number. Now, your task is telling me what position of the largest prime factor. The position of prime 2 is 1, prime 3 is 2, and prime 5 is 3, etc. Specially, LPF(1) = 0.

Input Each line will contain one integer n(0 < n < 1000000).

Output Output the LPF(n).

Sample Input 1 2 3 4 5

Sample Output 0 1 2 1 3

题解：

和省赛K题类似。素数筛法。更新位置。

代码：

#include <bits/stdc++.h> using namespace std; const int MAXN = 1000000; typedef long long LL; LL prime[MAXN+1]; void getPrime() { memset(prime,0,sizeof(prime)); int ans=0; for(int i=2;i<=MAXN;i++) { if(!prime[i]) { ans++; for(int j=i;j<MAXN;j+=i) prime[j]=ans; } } } int main() { getPrime(); LL n; while(scanf("%d",&n)!=EOF) { printf("%d\n",prime[n]); } return 0; }