Superprime Rib_特殊的质数肋骨_usaco1.5_codevs2080_dfs

DESCRIPTION

Butchering Farmer John’s cows always yields the best prime rib. You can tell prime ribs by looking at the digits lovingly stamped across them, one by one, by FJ and the USDA. Farmer John ensures that a purchaser of his prime ribs gets really prime ribs because when sliced from the right, the numbers on the ribs continue to stay prime right down to the last rib, e.g.:

 7  3  3  1

The set of ribs denoted by 7331 is prime; the three ribs 733 are prime; the two ribs 73 are prime, and, of course, the last rib, 7, is prime. The number 7331 is called a superprime of length 4.

Write a program that accepts a number N 1 <=N<=8 of ribs and prints all the superprimes of that length.

The number 1 (by itself) is not a prime number.

PROGRAM NAME: sprime

INPUT FORMAT

A single line with the number N.

OUTPUT FORMAT

The superprime ribs of length N, printed in ascending order one per line.

TRANSLATION

以最高位为起点，截取任何一段数都是质数的数被称为质数肋骨
给定n，求所有n位的质数肋骨

ANALYSIS

dfs生成每一位，一直保证当前数是质数肋骨就好了

CODE

/*
ID:wjp13241
PROG:sprime
LANG:C++
*/

#include 

using namespace std;

int n;

int prime(int x)
{
    if (x==1)
        return 0;
    for (int i=2;i*i<=x;i++)
        if(!(x%i))
            return 0;
    return 1;
}

void dfs(int dep,int x)
{
    if (!prime(x))
        return;
    if (dep==n+1)
        printf("%d\n",x);
    else
        for (int i=1;i<=9;i++)
            dfs(dep+1,x*10+i);
}

int main()
{
    freopen("sprime.in","r",stdin);
    freopen("sprime.out","w",stdout);

    scanf("%d",&n);
    dfs(1,0);

    fclose(stdin);
    fclose(stdout);
    return 0;
}

转载于:https://www.cnblogs.com/olahiuj/p/5781226.html