LeetCode-in-Java

906. Super Palindromes

Hard

Let’s say a positive integer is a super-palindrome if it is a palindrome, and it is also the square of a palindrome.

Given two positive integers left and right represented as strings, return the number of super-palindromes integers in the inclusive range [left, right].

Example 1:

Input: left = “4”, right = “1000”

Output: 4

Explanation: 4, 9, 121, and 484 are superpalindromes. Note that 676 is not a superpalindrome: 26 * 26 = 676, but 26 is not a palindrome.

Example 2:

Input: left = “1”, right = “2”

Output: 1

Constraints:

• 1 <= left.length, right.length <= 18
• left and right consist of only digits.
• left and right cannot have leading zeros.
• left and right represent integers in the range [1, 1018 - 1].
• left is less than or equal to right.

Solution

public class Solution {
    public int superpalindromesInRange(String left, String right) {
        long l = Long.parseLong(left);
        long r = Long.parseLong(right);
        int cnt = 0;
        long cur = 1;
        while (true) {
            long p1 = getPalindromeIncLastDigit(cur);
            long p2 = getPalindromeExcLastDigit(cur);
            long sq1 = p1 * p1;
            long sq2 = p2 * p2;
            if (sq2 > r) {
                break;
            }
            if (sq1 >= l && sq1 <= r && isPalindrome(sq1)) {
                cnt++;
            }
            if (sq2 >= l && isPalindrome(sq2)) {
                cnt++;
            }
            cur++;
        }
        return cnt;
    }

    private boolean isPalindrome(long val) {
        long construct = 0;
        if (val % 10 == 0 && val >= 10) {
            return false;
        }
        while (construct < val) {
            construct = construct * 10 + val % 10;
            val /= 10;
        }
        return construct == val || construct / 10 == val;
    }

    private long getPalindromeIncLastDigit(long val) {
        long copy = val;
        while (copy != 0) {
            val = val * 10 + copy % 10;
            copy /= 10;
        }
        return val;
    }

    private long getPalindromeExcLastDigit(long val) {
        long copy = val / 10;
        while (copy != 0) {
            val = val * 10 + copy % 10;
            copy /= 10;
        }
        return val;
    }
}

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