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

Note:

The range of n is [1,8].

package l479;/* * 面试场上正常情况应该就是用brute force，就是做点优化 * 关键在于快速的寻找下一个回文数字，然后判断是不是可以写成2个数的乘积 *  * 从小到大的回文数字是： * 9889，9779,9669,9559，。。。。 * 所以就只要关注前2个数字 */public class Solution {    public int largestPalindrome(int n) {        if(n == 1)return 9;        int maxHalf = (int) (Math.pow(10, n)-1);                for(int i=maxHalf-1; i>maxHalf/10; i--) {        long max = Long.valueOf(i + new StringBuilder().append(i).reverse().toString());                //判断这个max是否是 2个数的乘积        for(long j=maxHalf; j*j>=max; j--)        if(max % j == 0)        return (int) (max%1337);        }                return -1;    }}