PTA 1114 All-day C++ Realization of Simple Code

 

The picture above is from Sina Weibo, showing a very cool "Vegan Day": May 23, 2019. That is, not only 20190523is it a prime number itself, but any 3substring of it that ends with a number at the end is also a prime number.

In this question, you are asked to write a program to determine whether a given date is a "full vegetarian day".

Input format:

The input  yyyymmdd is given a date in the format of . The guaranteed date of the topic is between January 1, 0001 and December 31, 9999.

Output format:

Starting from the original date, in descending order of substring length, each line first outputs a substring and a space, and then outputs  Yes, if the number corresponding to the substring is a prime number, otherwise output  No. If the date is a vegan day, it is output on the last line  All Prime!.

Input sample 1:

20190523

Output sample 1:

20190523 Yes
0190523 Yes
190523 Yes
90523 Yes
0523 Yes
523 Yes
23 Yes
3 Yes
All Prime!

Input sample 2:

20191231

Output sample 2:

20191231 Yes
0191231 Yes
191231 Yes
91231 No
1231 Yes
231 No
31 Yes
1 No

Problem-solving ideas: 

Take out the corresponding string to judge whether it is a prime number

Code example:

#include <bits/stdc++.h>

using namespace std;

//素数判断
bool isPrime(int num) {
	if (num <= 1) {
		return false;
	}

	for (int i = 2; i <= sqrt(num); i++) {
		if (num % i == 0) {
			return false;
		}
	}
	return true;
}

int main() {
	string date;
	cin >> date;

	bool flag = true;
	for (int i = 0; i < date.length(); i++) {
		//从date的第i号位置开始往后取所有的字符给date_son
		string date_son = date.substr(i);

		int num = stoi(date_son);

		if (isPrime(num)) {
			cout << date_son << " " << "Yes\n";
		}
		else {
			cout << date_son << " " << "No\n";
			flag = false;
		}
	}

	if (flag) {
		cout << "All Prime!\n";
	}

	return 0;
}

operation result: