CODEWITHSUNDEEP
javaalgorithmperformancepalindrome
Some guy 101
Some guy 101

Reputation: 25

How to fix this Java palindrome algorithm?

Solution as suggested by MrSmith42: Error in the p for loop. Fixing that corrected it.

I tried writing the code for question four of ProjectEuler.net archives. Need to find the largest palindrome which is a product of two 3-digit numbers.

I understand that this code is not the most efficient. For one, it goes upto 999,999. When the max should not exceed 999*999 = 998,001. I want to just get done with the problem. But I don't know if I can use Strings or String Tokenizer for this problem.

public class Main {
    public static void main(String[] args) {
        List<Integer> arr = new ArrayList<>();
        int a = 100000, b = 10000, c =1000, d = 100, e = 10, f = 1;
        int m, n, p, q, s, t;
 //The plan is to increment the numbers by one, starting from 100,000 upto 999,999.
        for (m = 1; m <= 9; m++) {
            for (n = 0; n <= 9; n++) {
                for (p = 0; n <= 9; n++) {
                    for (q = 0; q <= 9; q++) {
                        for (s = 0; s <= 9; s++) {
                            for (t = 0; t <= 9; t++) {
                                if (t*a + s*b + q*c + p*d + n*e + m*f == m*a + n*b + p*c + q*d + s*e + t*f) {
                                    arr.add(m*a + n*b + p*c + q*d + s*e + f*t); }}}}}
            }
        }
        for (int x: arr)
            System.out.println(x);
    }
}

I am getting numbers with the format ST00TS. So, not all the palindromes are covered. I can't figure out where I messed up.

Upvotes: 0

Views: 99

Answers (1)

MrSmith42
MrSmith42

Reputation: 10151

There is a copy and paste errors in the loop-header:

for (p = 0; p <= 9; p++) {  // not  (p = 0; n <= 9; n++)

Upvotes: 2

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