usaco1.52Prime Palindromes

dfs搜前5位数 根据前面的算后面的

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  1 /*

  2  ID: your_id_here

  3  PROG: pprime

  4  LANG: C++

  5  */

  6 #include <iostream>

  7 #include<cstdio>

  8 #include<cstring>

  9 #include<cmath>

 10 #include<algorithm>

 11 using namespace std;

 12 int a,b,g;

 13 int kk[10000],f[20][20],tt,ff[100000];

 14 char s[20];

 15 int prime(int x)

 16 {

 17     int i,j,k,flag = 1;

 18     k = sqrt(x);

 19     for(i = 2 ; i <= k ; i++)

 20     {

 21         if(x%i==0)

 22         {

 23             flag = 0;

 24             break;

 25         }

 26     }

 27     return flag;

 28 }

 29 int palind(int k,char *ss)

 30 {

 31     int i,flag = 1;

 32     for(i = 1; i <= k ;i++)

 33     if(ss[i]!=ss[k-i+1])

 34     {

 35         flag = 0;

 36         break;

 37     }

 38     return flag;

 39 }

 40 void dfs(int v)

 41 {

 42     int i,y,s1 =0,s2 =0,s3 = 0,j;

 43     char str[20],str3[20];

 44     if(v>5)

 45     return ;

 46     for(i = 1; i <= v ; i++)

 47     str[i] = s[i];

 48     for(i = 1; i <= v ; i++)

 49     str3[i] = s[i];

 50     j = v;

 51     for(i = v+1 ; i <= 2*v ; i++)

 52     str[i] = s[j--];

 53     j = v-1;

 54     for(i = v+1 ; i < 2*v ; i++)

 55     str3[i] = s[j--];

 56     y = 1;

 57     for(i = v; i >= 1 ; i--)

 58     {

 59         s1+=y*(s[i]-'0');

 60         y = y*10;

 61     }

 62     y = 1;

 63     for(i = 2*v ; i >= 1 ; i--)

 64     {

 65         s2+=y*(str[i]-'0');

 66         y = y*10;

 67     }

 68     y = 1;

 69     for(i = 2*v-1 ; i >= 1 ; i--)

 70     {

 71         s3+=y*(str3[i]-'0');

 72         y = y*10;

 73     }

 74     if(s1>=a&&s1<=b)

 75     {

 76         if(palind(v,s)&&prime(s1))

 77         {

 78             if(s1<100000)

 79             {

 80                 if(!ff[s1])

 81                 {

 82                     g++;

 83                     kk[g] = s1;

 84                     ff[s1] = 1;

 85                 }

 86             }

 87             else

 88             {

 89                 g++;

 90                 kk[g] = s1;

 91             }

 92         }

 93     }

 94     if(s2>=a&&s2<=b)

 95     {

 96         if(palind(2*v,str)&&prime(s2))

 97         {

 98             if(s2<100000)

 99             {

100                 if(!ff[s2])

101                 {

102                     g++;

103                     kk[g] = s2;

104                     ff[s2] = 1;

105                 }

106             }

107             else

108             {

109 

110                 g++;

111                 kk[g] = s2;

112             }

113         }

114     }

115     if(s3>=a&&s3<=b)

116     {

117         if(palind(2*v-1,str3)&&prime(s3))

118         {

119 

120             if(s3<100000)

121             {

122                 if(!ff[s3])

123                 {

124                     g++;

125                     kk[g] = s3;

126                     ff[s3] = 1;

127                 }

128             }

129             else

130             {

131                 g++;

132                 kk[g] = s3;

133             }

134         }

135     }

136     if(s1>b)

137     return ;

138     for(i = 0 ; i <= 9 ; i++)

139     {

140         s[v+1] = i+'0';

141         dfs(v+1);

142     }

143 }

144 int main()

145 {

146     freopen("pprime.in","r",stdin);

147     freopen("pprime.out","w",stdout);

148     int i;

149     char num[20];

150     cin>>a>>b;

151     for(i = 1; i <= 9 ; i++)

152     {

153         s[1] = i+'0';

154         dfs(1);

155     }

156     sort(kk+1,kk+g+1);

157     for(i = 1; i <= g ; i++)

158     cout<<kk[i]<<endl;

159     fclose(stdin);

160     fclose(stdout);

161     return 0;

162 }