package ProjectEuler; /** * A palindromic number reads the same both ways. The largest palindrome made from the product of * two 2-digit numbers is 9009 = 91 × 99. * *

Find the largest palindrome made from the product of two 3-digit numbers. * *

link: https://projecteuler.net/problem=4 */ public class Problem04 { public static void main(String[] args) { assert solution1(10000) == -1; assert solution1(20000) == 19591; /* 19591 == 143*137 */ assert solution1(30000) == 29992; /* 29992 == 184*163 */ assert solution1(40000) == 39893; /* 39893 == 287*139 */ assert solution1(50000) == 49894; /* 49894 == 494*101 */ assert solution1(60000) == 59995; /* 59995 == 355*169 */ assert solution1(70000) == 69996; /* 69996 == 614*114 */ assert solution1(80000) == 79897; /* 79897 == 733*109 */ assert solution1(90000) == 89798; /* 89798 == 761*118 */ assert solution1(100000) == 99999; /* 100000 == 813*123 */ } private static int solution1(int n) { for (int i = n - 1; i >= 10000; --i) { String strNumber = String.valueOf(i); /* Test if strNumber is palindrome */ if (new StringBuilder(strNumber).reverse().toString().equals(strNumber)) { for (int divisor = 999; divisor >= 100; --divisor) { if (i % divisor == 0 && String.valueOf(i / divisor).length() == 3) { return i; } } } } return -1; /* not found */ } }