[UVa] 10235 - Simply Emirp

題目網址: http://goo.gl/u2rBsr

題意:
(from luckycat)


解 法: 建質數表。

TAG: Prime,

注意:

程式碼:

	/**
	* Tittle: 10235 - Simply Emirp
	* Author: Cheng-Shih, Wong
	* Date: 2015/05/25
	*/
	// include files
	#include <iostream>
	#include <cstdio>
	#include <cstring>
	using namespace std;
	// definitions
	#define FOR(i,a,b) for( int i=(a),_n=(b); i<=_n; ++i )
	#define clr(x,v) memset( x, v, sizeof(x) )
	#define N 10000005
	typedef long long ll;
	// declarations
	int n;
	bool isprime[N];
	// functions
	int revDig( int v )
	{
	int ret = 0;
	while( v ) {
	ret = (ret*10+v%10);
	v /= 10;
	}
	return ret;
	}
	// main function
	int main( void )
	{
	// init
	clr( isprime, true );
	isprime[0] = isprime[1] = false;
	for( ll i=2LL; i<=10000000LL; ++i ) if( isprime[i] ) {
	for( ll j=i*i; j<=10000000LL; j+=i )
	isprime[j] = false;
	}
	while( scanf( "%d", &n )==1 ) {
	// solve
	if( !isprime[n] ) printf( "%d is not prime.\n", n );
	else {
	if( isprime[revDig(n)] && n!=revDig(n) )
	printf( "%d is emirp.\n", n );
	else
	printf( "%d is prime.\n", n );
	}
	}
	return 0;
	}

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