hdu 1286 欧拉函数

求小于N的与N互质的数的个数

欧拉函数的应用

AC代码如下：

#include <iostream>#include <cstring>#include <cstdio>#include <algorithm>using namespace std;const int MAX_N = 32768+5;int num[MAX_N];int N;void init(){    memset( num, 0, sizeof( num ) );    for( int i = 2; i < MAX_N; i++ ){        if( num[i] == 0 ){            for( int j = i; j < MAX_N; j += i ){                if( num[j] == 0 )   num[j] = j;                num[j] = num[j] / i * ( i - 1 );            }        }    }}int main(){    int T;    init();    scanf( "%d", &T );    while( T-- ){        scanf( "%d", &N );        printf( "%d\n", num[N] );    }    return 0;}