LeetCode Solutions

			

class Solution {
 public:
  int primePalindrome(int N) {
    if (N <= 2)
      return 2;
    if (N == 3)
      return 3;
    if (N <= 5)
      return 5;
    if (N <= 7)
      return 7;
    if (N <= 11)
      return 11;

    int n = to_string(N).length();

    while (true) {
      for (const int num : getPalindromes(n))
        if (num >= N && isPrime(num))
          return num;
      ++n;
    }

    throw;
  }

 private:
  vector<int> getPalindromes(int n) {
    vector<int> palindromes;
    const int length = n / 2;

    for (int i = pow(10, length - 1); i < pow(10, length); ++i) {
      const string s = to_string(i);
      string reversedS = s;
      reverse(begin(reversedS), end(reversedS));
      for (int j = 0; j < 10; ++j)
        palindromes.push_back(stoi(s + to_string(j) + reversedS));
    }

    return palindromes;
  }

  bool isPrime(int num) {
    for (int i = 2; i < sqrt(num) + 1; ++i)
      if (num % i == 0)
        return false;

    return true;
  }
};

			

class Solution {
  public int primePalindrome(int N) {
    if (N <= 2)
      return 2;
    if (N == 3)
      return 3;
    if (N <= 5)
      return 5;
    if (N <= 7)
      return 7;
    if (N <= 11)
      return 11;

    int n = String.valueOf(N).length();

    while (true) {
      for (int num : getPalindromes(n))
        if (num >= N && isPrime(num))
          return num;
      ++n;
    }
  }

  private List<Integer> getPalindromes(int n) {
    List<Integer> palindromes = new ArrayList<>();
    int length = n / 2;

    for (int i = (int) Math.pow(10, length - 1); i < (int) Math.pow(10, length); ++i) {
      String s = String.valueOf(i);
      String reversedS = new StringBuilder(s).reverse().toString();
      for (int j = 0; j < 10; ++j)
        palindromes.add(Integer.valueOf(s + String.valueOf(j) + reversedS));
    }

    return palindromes;
  }

  private boolean isPrime(int num) {
    for (int i = 2; i < (int) Math.sqrt(num) + 1; ++i)
      if (num % i == 0)
        return false;

    return true;
  }
}

			

class Solution:
  def primePalindrome(self, N: int) -> int:
    def getPalindromes(n: int) -> int:
      length = n // 2
      for i in range(10**(length - 1), 10**length):
        s = str(i)
        for j in range(10):
          yield int(s + str(j) + s[::-1])

    def isPrime(num: int) -> bool:
      return not any(num % i == 0 for i in range(2, int(num**0.5 + 1)))

    if N <= 2:
      return 2
    if N == 3:
      return 3
    if N <= 5:
      return 5
    if N <= 7:
      return 7
    if N <= 11:
      return 11

    n = len(str(N))

    while True:
      for num in getPalindromes(n):
        if num >= N and isPrime(num):
          return num
      n += 1