USACO 1.5 Prime Palindromes
2011-05-02 14:13
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/* ID: jiafeim1 PROG: pprime LANG: C++ */ #include <iostream> #include <fstream> #include <algorithm> using namespace std; #include <cmath> long pp[200000]; long top = 0; bool check(long num) { if(num%2 == 0) return false; long end = std::sqrt((float)num)+1; for(int i=3;i<=end;i+=2) { if(num%i==0) return false; } return true; } int main() { ofstream fout ("pprime.out"); ifstream fin ("pprime.in"); pp[0] = 5; pp[1] = 7; pp[2] = 11; top = 3; for (int a1 = 1; a1 <= 9; a1 += 2) { for (int a2 = 0 ; a2 <= 9; ++a2) { pp[top++] = a1 + a2 * 10 + a1 * 100; } } for (int a1 = 1; a1 <= 9; a1 += 2) { for (int a2 = 0 ; a2 <= 9; ++a2) { for (int a3 = 0; a3 <= 9; ++a3) { pp[top++] = a1 + a2 * 10 + a3 * 100 + a2 * 1000 + a1 * 10000; } } } for (int a1 = 1; a1 <= 9; a1 += 2) { for (int a2 = 0 ; a2 <= 9; ++a2) { for (int a3 = 0; a3 <= 9; ++a3) { for (int a4 = 0 ; a4 <= 9 ; ++a4) { pp[top++] = a1 + a2 * 10 + a3 * 100 + a4 * 1000 + a3 * 10000 + a2 * 100000 + a1 * 1000000; } } } } long min,max; fin>>min>>max; int start; for(start = 0;start!=top;++start) { if(pp[start]>=min) break; } for(;start!=top;++start) { if(pp[start]>max) break; if(check(pp[start])) fout<<pp[start]<<endl; } fin.close(); fout.close(); return 0; }
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