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.
To check if a number in Javascript is palindrome, we can convert it to String, then split into char array, reverse the array, and join as a string, then a palindrome is a string that its reverse is the same.
1 2 3 4 5 6 7 8 9 10 11 12 13 | let ans = 0; for (let i = 999; i >= 100; i --) { for (let j = 999; j >= 100; j --) { let num = i * j; let s = String(num); let rs = s.split('').reverse().join(''); if (s === rs) { ans = Math.max(ans, num); } } } console.log(ans); |
let ans = 0; for (let i = 999; i >= 100; i --) { for (let j = 999; j >= 100; j --) { let num = i * j; let s = String(num); let rs = s.split('').reverse().join(''); if (s === rs) { ans = Math.max(ans, num); } } } console.log(ans);
Two loops each range from 100 to 999 for 3-digit number. Then we check the product and record the maximum palindrome.
The answer is: 906609.
–EOF (The Ultimate Computing & Technology Blog) —
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Is there a better algorithm?
Another idea is to go through all 6 digit product numbers which are also palindrome. And check if it could be expressed as two 3-digit product.