The Euler function[HDU2824]

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The Euler function
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 6018 Accepted Submission(s): 2539

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 Input
3 100

Sample Output
3042

3000000的数据范围，没想到是直接加的......贡献一次MLE。

#include <stdio.h>
#include <string.h>
int euler[3000010];
void Euler_Sieve_Method(int * euler, int n) {
    euler[1] = 1;
    for (int i = 2; i < n; i++) {
        euler[i] = i;
    }
    for (int i = 2; i < n; i++) {
        if (euler[i] == i) {
            for (int j = i; j < n; j += i) {
                euler[j] = euler[j] / i * (i - 1);
            }
        }
    }
}
int main() {
    Euler_Sieve_Method(euler, 3000005);
    int a, b;
    while (scanf("%d%d", &a, &b) != EOF) {
        __int64 s = 0;
        for (int i = a; i <= b; i++) {
            s += euler[i];
        }
        printf("%I64d\n", s);
    }
    return 0;
}

View Code

The Euler function[HDU2824]

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原文地址：http://www.cnblogs.com/dramstadt/p/6254428.html