_leetcode-479

Largest Palindrome Product

Find the largest palindrome made from the product of two n-digit numbers.

Since the result could be very large, you should return the largest palindrome mod 1337.

Example:

Input: 2

Output: 987

Explanation: 99 x 91 = 9009, 9009 % 1337 = 987

此题较难，我一开始没读懂题，到现在还是有些没有理解，所以下面是借鉴别人的解法。

此题题意是求两个n位数的最大回文，n是输入，输出有些数太大所以对1337取余。什么是回文？就是数字左右两边对称，比如123321,1221,987789都是回文。

java代码:

public class Solution{
    public int largestPalindrome(int n) {
        long max = (long)Math.pow(10, n) - 1;
        long min = max / 10+1; 
        
        for (long h = max; h > min; h--) {
            long left = h, right = 0;
            for (long i = h; i != 0;  i /= 10){
                right = right * 10 + i % 10;//9   99     8   89
                left*= 10;                  //990 9900   980 9800
            }
            
            long palindrom = left + right;  //9999  9889  // construct the palindrome
            for (long i = max; i > min; i--) {
                long j = palindrom / i;
                if (j > i || j <= min) break;     // terminate if the other number is greater than current number or is not an n-digit number
                if (palindrom % i == 0) return (int)(palindrom % 1337); // found if current number is a factor
            }
        }

        return 9;    // account for case n = 1
    }
}