2323 Emirp（哈尔滨理工大学）

最新推荐文章于 2023-11-03 11:58:18 发布

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Emirp

Time Limit: 5000 MS

Memory Limit: 100000 K

Total Submit: 143(59 users)

Total Accepted: 61(55 users)

Rating:

Special Judge: No

Description

An emirp (prime spelled backwards) is a prime number that results in a different prime when its decimal digits are reversed.

The first five emirps are 13, 17, 31, 37, 71

Now Kim want to know the kth emirp. Help him.

Input

The first line is an integer T, describes the number of tests. Then T tests.

In each test, one line an integer k.

Output

For each test, output the kth emirp.

Sample Input

Sample Output

13
17
31

Hint

T<=10000

k<=1000

思路：就是找大于十的数使其本身和其反置都为素数，并且本身和其反置数不能相同。

代码：

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define fo(i,a,b) for(int i=a;i<=b;i++)
#define fd(i,a,b) for(int i=a;i>=b;i--)
#define inf 0x3f3f3f3f
#define ll long long
#define mem(a,b) memset(a,b,sizeof(a))
using namespace std;
int a[1009],k,n;
int isprim(int x)
{

    for(int i=2; i*i<=x; i++)
    {
        if(x%i==0)
        {
            return 0;
        }
    }
    return 1;
}
void init()
{
    k=0;
    for(int i=13; i<=70529; i++)
    {
        int sum=0;
        int temp=i;
        while(temp>0)
        {
            int flag=temp%10;
            temp/=10;
            sum=sum*10+flag;
        }//将数反置
        if(isprim(i)==1&&isprim(sum)==1&&i!=sum)//都为素数且不相等
        {
            k++;
            if(k==n)
            {
                printf("%d\n",i);
                break;
            }
        }

    }
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        init();
        // printf("%d\n",a[n-1]);
    }
}

感觉是很正确的，但是提交超时，所以就用这个程序打了一个表，然后就过了，证明代码是没问题的只是时间复杂度比较大，然后还是不知道怎样优化时间复杂度，，，

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define fo(i,a,b) for(int i=a;i<=b;i++)
#define fd(i,a,b) for(int i=a;i>=b;i--)
#define inf 0x3f3f3f3f
#define ll long long
#define mem(a,b) memset(a,b,sizeof(a))
using namespace std;
int main()
{
    int a[1009]={0,13,17,31,37,71,73,79,97,107,113,149,157,167,179,199,311,337,347,359,389,701,709,733,739,743,751,761,769,907,937,941,953,967,971,983,991,1009,1021,1031,1033,1061,1069,1091,1097,1103,1109,1151,1153,1181,1193,1201,1213,1217,1223,1229,1231,1237,1249,1259,1279,1283,1301,1321,1381,1399,1409,1429,1439,1453,1471,1487,1499,1511,1523,1559,1583,1597,1601,1619,1657,1669,1723,1733,1741,1753,1789,1811,1831,1847,1867,1879,1901,1913,1933,1949,1979,3011,3019,3023,3049,3067,3083,3089,3109,3121,3163,3169,3191,3203,3221,3251,3257,3271,3299,3301,3319,3343,3347,3359,3371,3373,3389,3391,3407,3433,3463,3467,3469,3511,3527,3541,3571,3583,3613,3643,3697,3719,3733,3767,3803,3821,3851,3853,3889,3911,3917,3929,7027,7043,7057,7121,7177,7187,7193,7207,7219,7229,7253,7297,7321,7349,7433,7457,7459,7481,7507,7523,7529,7547,7561,7577,7589,7603,7643,7649,7673,7681,7687,7699,7717,7757,7817,7841,7867,7879,7901,7927,7949,7951,7963,9001,9011,9013,9029,9041,9103,9127,9133,9161,9173,9209,9221,9227,9241,9257,9293,9341,9349,9403,9421,9437,9439,9467,9479,9491,9497,9521,9533,9547,9551,9601,9613,9643,9661,9679,9721,9749,9769,9781,9787,9791,9803,9833,9857,9871,9883,9923,9931,9941,9967,10007,10009,10039,10061,10067,10069,10079,10091,10151,10159,10177,10247,10253,10273,10321,10333,10343,10391,10429,10453,10457,10459,10487,10499,10613,10639,10651,10711,10739,10781,10853,10859,10867,10889,10891,10909,10939,10987,10993,11003,11057,11071,11083,11149,11159,11161,11197,11243,11257,11329,11353,11423,11447,11489,11497,11551,11579,11587,11593,11621,11657,11677,11699,11701,11717,11719,11731,11777,11779,11783,11789,11833,11839,11897,11903,11909,11923,11927,11933,11939,11953,11959,11969,11971,11981,12071,12073,12107,12109,12113,12119,12149,12227,12241,12253,12269,12289,12301,12323,12373,12437,12491,12547,12553,12577,12611,12619,12641,12659,12689,12697,12713,12743,12757,12763,12799,12809,12829,12841,12893,12907,12919,12983,13009,13043,13147,13151,13159,13163,13259,13267,13291,13297,13337,13441,13457,13469,13477,13499,13513,13523,13553,13591,13597,13619,13693,13697,13709,13711,13751,13757,13759,13781,13789,13829,13841,13873,13903,13933,13963,14029,14057,14071,14081,14087,14107,14143,14153,14177,14207,14221,14251,14293,14303,14323,14327,14387,14423,14431,14447,14449,14479,14519,14549,14551,14557,14563,14591,14593,14621,14629,14633,14657,14713,14717,14821,14831,14843,14879,14891,14897,14923,14929,14939,14947,14957,15013,15053,15091,15101,15131,15139,15149,15227,15241,15263,15289,15299,15307,15349,15377,15383,15461,15493,15497,15511,15527,15541,15601,15643,15649,15661,15667,15679,15683,15731,15733,15737,15791,15803,15907,15919,15937,15973,16001,16007,16063,16073,16103,16111,16127,16193,16217,16223,16249,16267,16427,16433,16451,16453,16481,16493,16547,16567,16573,16603,16651,16691,16699,16729,16747,16763,16829,16879,16883,16937,16943,16979,17011,17021,17033,17041,17047,17117,17203,17207,17209,17383,17393,17417,17443,17467,17477,17491,17519,17573,17579,17599,17627,17669,17681,17683,17713,17737,17747,17749,17827,17839,17863,17903,17909,17911,17923,17939,17959,18013,18041,18077,18089,18133,18169,18191,18199,18253,18269,18307,18329,18353,18379,18413,18427,18439,18461,18539,18593,18637,18671,18691,18701,18719,18731,18743,18749,18757,18773,18787,18803,18859,18899,18911,18913,19001,19013,19037,19051,19163,19181,19219,19231,19237,19249,19301,19333,19403,19421,19423,19471,19477,19489,19531,19541,19543,19553,19577,19661,19681,19687,19697,19751,19759,19763,19793,19801,19813,19841,19913,19973,30011,30029,30059,30139,30161,30197,30223,30259,30271,30319,30323,30341,30367,30467,30491,30517,30529,30539,30557,30593,30643,30649,30661,30757,30809,30851,30853,30859,30881,30911,30931,30949,30971,30983,31033,31051,31063,31069,31081,31091,31121,31139,31183,31193,31223,31259,31267,31277,31307,31327,31393,31481,31531,31543,31601,31627,31643,31649,31721,31723,31741,31771,31799,31859,31873,31891,31907,31957,31963,31981,31991,32009,32077,32099,32143,32173,32189,32203,32213,32233,32257,32261,32299,32303,32321,32341,32353,32369,32377,32411,32441,32467,32479,32491,32497,32531,32537,32563,32579,32633,32647,32687,32693,32713,32749,32783,32869,32887,32911,32933,32939,32941,32971,32983,32999,33013,33029,33049,33071,33181,33199,33223,33287,33301,33317,33329,33391,33461,33589,33617,33623,33641,33751,33767,33809,33811,33857,33863,33911,33923,33931,34031,34123,34129,34141,34147,34159,34211,34267,34273,34301,34367,34469,34471,34513,34549,34583,34589,34591,34603,34613,34651,34673,34687,34721,34757,34781,34807,34841,34847,34897,34919,34961,34963,35027,35051,35069,35083,35099,35117,35129,35141,35149,35159,35201,35221,35227,35257,35267,35281,35311,35317,35323,35327,35363,35381,35401,35419,35437,35447,35461,35521,35531,35537,35569,35591,35729,35801,35803,35911,35969,35983,35993,36013,36037,36061,36097,36107,36109,36131,36187,36191,36209,36217,36251,36269,36277,36353,36373,36467,36473,36479,36523,36541,36599,36607,36721,36739,36761,36791,36809,36833,36871,36877,36913,36931,36943,36973,37021,37061,37123,37199,37201,37243,37307,37309,37321,37363,37379,37409,37463,37489,37507,37547,37549,37561,37571,37589,37619,37643,37781,37813,37831,37847,37889,37897,37951,37963,37991,37997,38011,38039,38053,38113,38119,38219,38239,38287,38327,38329,38351,38371,38377,38393,38449,38459,38543,38557,38629,38639,38651,38671,38707,38711,38723,38737,38861,38867,38903,38917,38921,38923,38953,38977,38993,39047,39113,39119,39157,39161,39217,39241,39313,39359,39371,39383,39397,39419,39439,39451,39461,39503,39511,39541,39581,39623,39631,39709,39749,39791,39799,39821,39827,39829,39839,39869,39877,39887,39901,39929,39953,39983,39989,70001,70009,70061,70079,70121,70141,70163,70241,70249,70271,70289,70313,70327,70351,70373,70381,70439,70457,70489,70529};
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int n;
        scanf("%d",&n);
        printf("%d\n",a[n]);
    }
}