Thu Mar 14 01:20:15 JST 2013

-- test.hs
fact 0 = 1
fact n = n * fact (n-1)
main = getLine >>= print.fact.read

{-
$ time ./test < input
815915283247897734345611269596115894272000000000

real    0m0.005s
user    0m0.000s
sys     0m0.004s
$ time ./test < input
815915283247897734345611269596115894272000000000

real    0m0.006s
user    0m0.000s
sys     0m0.000s
-}

;; test.scm
(define (fact n)
    (if (zero? n) 1
        (* n (fact (- n 1)))))
(print (fact (read)))

#|
$ time gosh test.scm < input
815915283247897734345611269596115894272000000000

real    0m0.029s
user    0m0.012s
sys     0m0.012s
$ time gosh test.scm < input
815915283247897734345611269596115894272000000000

real    0m0.029s
user    0m0.016s
sys     0m0.004s
|#

// test.js (多倍長演算の一部を実装してるので長い)
function mult(n, bi) {
    var base = 19;
    bi = bi.map(function(s){return s*n});
    for (var i=0;i<bi.length;++i) {
        var s = bi[i] + "";
        if (s.length > base) {
            var len = s.length;
            bi[i] = +s.slice(len-base, len);
            if ((i+1) in bi)
                bi[i+1] += +s.slice(0, len-base);
            else
                bi[i+1] = +s.slice(0, len-base);
        }
    }
    return bi;
}
function show(bi) {
    var str = "", len = bi.length;
    for (var i=0;i<len;++i)
        str += bi[len-i-1];
    return str;
}
function fact(n){
    return n==0 ? [1] : mult(n, fact(n-1));
}
console.log(show(fact(+require("fs").readFileSync("/dev/stdin","utf-8"))))