hdu 2824(歐拉函數)

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The Euler function

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 5235    Accepted Submission(s): 2225

Problem Description The Euler function phi is an important kind of function in number theory, (n) represents the amount of the numbers which are smaller than n and coprime to n, and this function has a lot of beautiful characteristics. Here comes a very easy question: suppose you are given a, b, try to calculate (a)+ (a+1)+....+ (b) 

 

Input There are several test cases. Each line has two integers a, b (2<a<b<3000000). 

 

Output Output the result of (a)+ (a+1)+....+ (b) 

 

Sample Input3 100 

 

Sample Output3042 歐拉函數模板題，不能開兩個數組，會逾時。

#include <stdio.h>#include <string.h>#include <algorithm>#include <iostream>#include <math.h>using namespace std;typedef long long LL;const int N =3000005;LL euler[N];//LL sum[N];void getEuler(){    memset(euler,0,sizeof(euler));    euler[1] = 1;    for(int i = 2; i <= N; i++){        if(!euler[i])            for(int j = i; j <= N; j+= i)            {                if(!euler[j])                    euler[j] = j;                euler[j] = euler[j]/i*(i-1);            }        //sum[i]=sum[i-1]+(LL)euler[i];    }}int main(){    getEuler();    int a,b;    while(~scanf("%d%d",&a,&b)){        LL sum = 0;        for(int i=a;i<=b;i++){            sum+=euler[i];        }        printf("%lld\n",sum);    }    return 0;}

 

hdu 2824(歐拉函數)