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866. Prime Palindrome

Description

Given an integer n, return the smallest prime palindrome greater than or equal to n.

An integer is prime if it has exactly two divisors: 1 and itself. Note that 1 is not a prime number.

  • For example, 2, 3, 5, 7, 11, and 13 are all primes.

An integer is a palindrome if it reads the same from left to right as it does from right to left.

  • For example, 101 and 12321 are palindromes.

The test cases are generated so that the answer always exists and is in the range [2, 2 * 108].

 

Example 1:

Input: n = 6
Output: 7

Example 2:

Input: n = 8
Output: 11

Example 3:

Input: n = 13
Output: 101

 

Constraints:

  • 1 <= n <= 108

Solutions

Solution 1

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class Solution:
    def primePalindrome(self, n: int) -> int:
        def is_prime(x):
            if x < 2:
                return False
            v = 2
            while v * v <= x:
                if x % v == 0:
                    return False
                v += 1
            return True

        def reverse(x):
            res = 0
            while x:
                res = res * 10 + x % 10
                x //= 10
            return res

        while 1:
            if reverse(n) == n and is_prime(n):
                return n
            if 10**7 < n < 10**8:
                n = 10**8
            n += 1

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class Solution {
    public int primePalindrome(int n) {
        while (true) {
            if (reverse(n) == n && isPrime(n)) {
                return n;
            }
            if (n > 10000000 && n < 100000000) {
                n = 100000000;
            }
            ++n;
        }
    }

    private boolean isPrime(int x) {
        if (x < 2) {
            return false;
        }
        for (int v = 2; v * v <= x; ++v) {
            if (x % v == 0) {
                return false;
            }
        }
        return true;
    }

    private int reverse(int x) {
        int res = 0;
        while (x != 0) {
            res = res * 10 + x % 10;
            x /= 10;
        }
        return res;
    }
}

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class Solution {
public:
    int primePalindrome(int n) {
        while (1) {
            if (reverse(n) == n && isPrime(n)) return n;
            if (n > 10000000 && n < 100000000) n = 100000000;
            ++n;
        }
    }

    bool isPrime(int x) {
        if (x < 2) return false;
        for (int v = 2; v * v <= x; ++v)
            if (x % v == 0)
                return false;
        return true;
    }

    int reverse(int x) {
        int res = 0;
        while (x) {
            res = res * 10 + x % 10;
            x /= 10;
        }
        return res;
    }
};

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func primePalindrome(n int) int {
    isPrime := func(x int) bool {
        if x < 2 {
            return false
        }
        for v := 2; v*v <= x; v++ {
            if x%v == 0 {
                return false
            }
        }
        return true
    }

    reverse := func(x int) int {
        res := 0
        for x != 0 {
            res = res*10 + x%10
            x /= 10
        }
        return res
    }
    for {
        if reverse(n) == n && isPrime(n) {
            return n
        }
        if n > 10000000 && n < 100000000 {
            n = 100000000
        }
        n++
    }
}

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