usaco——pprime

最新推荐文章于 2018-09-05 23:34:09 发布

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最新推荐文章于 2018-09-05 23:34:09 发布

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分类专栏： usaco 文章标签： output numbers file input list

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本文介绍了一个程序设计问题：找出指定范围内的所有素回文数。素回文数是指既是素数又是回文数的整数。文章提供了一个C++程序示例，用于生成两个给定数值之间的所有素回文数，并按升序输出。

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Prime Palindromes

The number 151 is a prime palindrome because it is both a prime number and a palindrome (it is the same number when read forward as backward). Write a program that finds all prime palindromes in the range of two supplied numbers a and b (5 <= a < b <= 100,000,000); both a and b are considered to be within the range .

PROGRAM NAME: pprime

INPUT FORMAT

Line 1:

Two integers, a and b

SAMPLE INPUT (file pprime.in)

5 500

OUTPUT FORMAT

The list of palindromic primes in numerical order, one per line.

SAMPLE OUTPUT (file pprime.out)

HINTS (use them carefully!)

#include <iostream> #include <fstream> using namespace std; int memory=0; ofstream fout("sprime.out"); ifstream fin("sprime.in"); bool isPrime(int num) { int divisor = 3; int testLimit = num; if(num==1) return false; if(num==2) return true; if (num % 2 == 0) return false; while ( testLimit > divisor ) { if ( num % divisor == 0 ) { return false; } testLimit = num / divisor; divisor += 2; } return true; } void solve(int a) { if(a>0) for(int i=1; i<10; i++) { memory=10*memory+i; if(isPrime(memory))if(a>1) solve(a-1);else fout<<memory<<endl; memory=(memory-i)/10;} } int main() { int a; fin>>a; solve(a); return 0; }