palin.wsf

# Sphere Online Judge
# Problem 5: PALIN - The Next Palindrome
# https://www.spoj.com/problems/PALIN/

    "@bool" import
    "@int"  import
    "@math" import

    0 ^ readi retrieve
.loop:
    1- ^ jn .end
    0 ^ readi retrieve
    1+ call find_pal printi '\n' printc
    jmp .loop
.end:
    drop end

# find_pal returns the smallest base-10 palindrome greater than or equal
# to n.
# (n -- pal)
find_pal:
    ^ call digit_count
    10 ^1 2/ **
    swap 2% jz .find_pal_even
    2dup / # upper
    ^
    ^2 10* ^4 ^1 % + # lower with leading 1
    10 call int.reverse_digits 10/
    < + # upper++ if reverse(lower) > upper
    10 call int.make_palindrome_odd
    2slide ret
.find_pal_even:
    2dup / # upper
    ^
    ^2 ^4 ^1 % + # lower with leading 1
    10 call int.reverse_digits 10/
    < + # upper++ if reverse(lower) > upper
    10 call int.make_palindrome_even
    2slide ret

# digit_count returns the number of base-10 digits in n.
# (n -- count)
digit_count:
    0
.digit_count_loop:
    swap ^ jz .digit_count_ret
    10/ swap 1+
    jmp .digit_count_loop
.digit_count_ret:
    drop ret