TheAlgorithms-Java/ProjectEuler/Problem04.java at master · windNight/TheAlgorithms-Java · GitHub

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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.

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

* <p>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 */

}

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