1152 Google Recruitment （20 分)

谁践踏了优雅 2022-03-02 15:54 159阅读 0赞

In July 2004, Google posted on a giant billboard along Highway 101 in Silicon Valley (shown in the picture below) for recruitment. The content is super-simple, a URL consisting of the first 10-digit prime found in consecutive digits of the natural constant e. The person who could find this prime number could go to the next step in Google's hiring process by visiting this website.

![prime.jpg][]

The natural constant e is a well known transcendental number（超越数）. The first several digits are: e = 2.71828182845904523536028747135266249775724709369995957496696762772407663035354759457138217852516642**7427466391**932003059921... where the 10 digits in bold are the answer to Google's question.

Now you are asked to solve a more general problem: find the first K-digit prime in consecutive digits of any given L-digit number.

### Input Specification: ###

Each input file contains one test case. Each case first gives in a line two positive integers: L (≤ 1,000) and K (< 10), which are the numbers of digits of the given number and the prime to be found, respectively. Then the L-digit number N is given in the next line.

### Output Specification: ###

For each test case, print in a line the first K-digit prime in consecutive digits of N. If such a number does not exist, output `404` instead. Note: the leading zeroes must also be counted as part of the K digits. For example, to find the 4-digit prime in 200236, 0023 is a solution. However the first digit 2 must not be treated as a solution 0002 since the leading zeroes are not in the original number.

### Sample Input 1: ###

20 5
    23654987725541023819

### Sample Output 1: ###

49877

### Sample Input 2: ###

10 3
    2468024680

### Sample Output 2: ###

404

题意：给一个长度为L的数字，找其中一段长度为K的数字为素数，前导0也算。

思路：暴力跑每个可能的数，判断是否为素数~在输出的时候记得要把前导0也输出，所以用int判断是否为素数，但是存的话是用String存的，方便输出~

#include<stdio.h>
    #include<string.h>
    #include<math.h>
    #include<iostream>
    #include<string>
    #include<sstream>
    #include<algorithm>
    #include<map>
    #include<set>
    #include<queue>
    #include<stack>
    #include<vector>
    using namespace std;
    #define inf 0x3f3f3f3f
    #define LL long long
    char a[1005];
    int prime(int x)
    {
    	if(x==0||x==1) return 0;
    	for(int i=2;i<sqrt(x);i++)
    	{
    		if(x%i==0)
    		{
    			return 0;
    		}
    	}
    	return 1;
    }
    int main()
    {
    	int n,k,i,j,l,s,f=0; 
    	scanf("%d%d",&n,&k);
    	scanf("%s",a);
    	for(i=0;i<n-k+1;i++)
    	{
    		//if(a[i]=='0')continue;
    		s=0;
    		string ss="";
    		for(j=i;j<i+k;j++)
    		{
    			s=s*10+(a[j]-'0');
    			ss+=a[j];
    		}
    		//cout<<s<<endl;
    		if(prime(s)==1)
    		{
    			cout<<ss<<endl;
    			//printf("%d\n",s);
    			f=1;
    			break;
    		}
    	}
    	if(f==0)
    	printf("404\n");
    }

[prime.jpg]: /images/20220302/6977727a766a4fed9721438339312745.png