UVA 11426 欧拉函数 + 递推

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code

import java.util.*;import static java.lang.System.*;public class Main{    static final int N = 4100000;    /**static long c;*/    static long[] phi = new long[N];    static long[] f = new long[N];    static long[] s = new long[N];    public static void main(String[] args){        Scanner in = new Scanner(System.in);        init();        while(in.hasNext()){            int n = in.nextInt();            if(n == 0) break;            out.println(s[n]);        }        in.close();    }    public static void init(){        for(int i = 0; i < N; ++i){            phi[i] = 0; s[i] = 0;            f[i] = 0;        }        phi[1] = 1;        for(int i = 2; i < N; ++i)            if(phi[i] == 0)                for(int j = i; j < N; j += i){                        if(phi[j] == 0) phi[j] = j;                        phi[j] = phi[j] / i * (i - 1);                }        for(int i = 1; i < N; ++i)            for(int j = i + i; j < N; j += i)                f[j] += i * phi[j / i];        for(int i = 2; i < N; ++i)            s[i] = s[i - 1] + f[i];    }}

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