FilesExpand file tree

 master

/

Problem004.js

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

44 lines (41 loc) · 1.16 KB

 master

/

Problem004.js

Top

File metadata and controls

• Code
• Blame

44 lines (41 loc) · 1.16 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

// https://projecteuler.net/problem=4

/* 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.

*/

export const largestPalindromic = (digits) => {

let i

let n

let m

let d

let limit

let number = 0

for (i = 1; i < digits; i++) {

number = 10 * number + 9

}

const inf = number // highest (digits - 1) number, in this example highest 2 digit number

const sup = 10 * number + 9 // highest (digits) number, in this example highest 3 digit number

const isPalindromic = (n) => {

let p = 0

const q = n

let r

while (n > 0) {

r = n % 10

p = 10 * p + r

n = Math.floor(n / 10)

}

return p === q // returning whether the number is palindromic or not

}

for (n = sup * sup, m = inf * inf; n > m; n--) {

if (isPalindromic(n)) {

limit = Math.ceil(Math.sqrt(n))

d = sup

while (d >= limit) {

if (n % d === 0 && n / d > inf) {

return n

}

d -= 1

}

}

}

return NaN // returning not a number, if any such case arise

}