LeetCode-in-Java

3765. Complete Prime Number

Medium

You are given an integer num.

A number num is called a Complete Prime Number if every prefix and every suffix of num is prime.

Return true if num is a Complete Prime Number, otherwise return false.

Note:

• A prefix of a number is formed by the first k digits of the number.
• A suffix of a number is formed by the last k digits of the number.
• Single-digit numbers are considered Complete Prime Numbers only if they are prime.

Example 1:

Input: num = 23

Output: true

Explanation:

• Prefixes of num = 23 are 2 and 23, both are prime.
• Suffixes of num = 23 are 3 and 23, both are prime.
• All prefixes and suffixes are prime, so 23 is a Complete Prime Number and the answer is true.

Example 2:

Input: num = 39

Output: false

Explanation:

• Prefixes of num = 39 are 3 and 39. 3 is prime, but 39 is not prime.
• Suffixes of num = 39 are 9 and 39. Both 9 and 39 are not prime.
• At least one prefix or suffix is not prime, so 39 is not a Complete Prime Number and the answer is false.

Example 3:

Input: num = 7

Output: true

Explanation:

• 7 is prime, so all its prefixes and suffixes are prime and the answer is true.

Constraints:

• 1 <= num <= 109

Solution

public class Solution {
    private boolean isPrime(int n) {
        if (n != 2 && n % 2 == 0) {
            return false;
        }
        for (int i = 3; i * i <= n; i += 2) {
            if (n % i == 0) {
                return false;
            }
        }
        return true;
    }

    public boolean completePrime(int num) {
        int y = 0;
        int z = 1;
        int x = num;
        while (x > 0) {
            y = z * (x % 10) + y;
            if (y == 1 || !isPrime(y)) {
                return false;
            }
            if (x == 1 || !isPrime(x)) {
                return false;
            }
            x /= 10;
            z *= 10;
        }
        return true;
    }
}

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