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Prime Palindrome in C++
Suppose we have to find the smallest prime palindrome that is greater than or equal to N. So if the N is 13, then the smallest palindrome will be 101.
To solve this, we will follow these steps −
If N is in range 8 to 11, then return 11
for i in range 1 to 99999
s := i as a string
r := s
reverse r
num := concatenate s and substring of r from index 1, then convert to number
if num >= N and num is prime, then return num
return 0
Let us see the following implementation to get better understanding −
Example
#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
bool isPrime(int n){
if(n % 2 == 0 && n > 2) return false;
for(int i = 3; i * i <= n; i++){
if(n % i == 0) return false;
}
return n != 1 && n != 0;
}
int primePalindrome(int N) {
if(8 <= N && N <= 11) return 11;
for(int i = 1; i < 100000; i++){
string s = to_string(i);
string r = s;
reverse(r.begin(), r.end());
int num = stoi(s + r.substr(1));
if(num >= N && isPrime(num)) return num;
}
return 0;
}
};
main(){
Solution ob;
cout << (ob.primePalindrome(105));
}Input
105
Output
131
Updated on: 30-Apr-2020
715 Views
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