HDU 2824 The Euler function 題解

標籤：des   style   blog   color   使用   2014   

求區間的euler數值，自然使用篩子法了。

Problem DescriptionThe 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) 
InputThere are several test cases. Each line has two integers a, b (2<a<b<3000000). 
OutputOutput the result of (a)+ (a+1)+....+ (b) 
Sample Input

3 100

 
Sample Output

3042

#include <stdio.h>const int MAX_SZIE = 3000001;__int64 phi[MAX_SZIE] = {0};void eulerPhi(){for (int i = 2; i < MAX_SZIE; i++){if (!phi[i]){for (int j = i; j < MAX_SZIE; j += i){if (!phi[j]) phi[j] = j;phi[j] = phi[j] / i * (i - 1);}}}for (int i = 3; i < MAX_SZIE; i++){phi[i] += phi[i-1];}}int main(){eulerPhi();int a, b;while (scanf("%d %d", &a, &b) != EOF){printf("%I64d\n", phi[b] - phi[a-1]);}return 0;}