Project Euler Problem 99

http://projecteuler.net/problem=99

Largest exponential

Problem 99

Comparing two numbers written in index form like 2¹¹ and 3⁷ is not difficult, as any calculator would confirm that 2¹¹ = 2048 3⁷ = 2187.

However, confirming that 632382⁵¹⁸⁰⁶¹ 519432⁵²⁵⁸⁰⁶ would be much more difficult, as both numbers contain over three million digits.

Using base_exp.txt (right click and 'Save Link/Target As...'), a 22K text file containing one thousand lines with a base/exponent pair on each line, determine which line number has the greatest numerical value.

NOTE: The first two lines in the file represent the numbers in the example given above.

Answer:

709

Racket

#lang racket
(require net/url)
(define port
  (get-pure-port
   (string->url "http://projecteuler.net/project/base_exp.txt")))

(define max 0)
(define maxlinenum 0)
(let loop ([linenum 1])
  (define line (read-line port)) 
  (when (not (eof-object? line))
    (displayln linenum)
    (define pair (string-split line ","))
    (define num (* (string->number (second pair))
                   (log (string->number (first pair)))))
    (when (> num max) (set! max num) (set! maxlinenum linenum))
    (loop (add1 linenum))))

(displayln maxlinenum)